I‘ve heard that a couple of times now - but don’t want to incorporate unless I am really sure that I will be staying in Taiwan 5 years+. But definitely want to keep that option open!
How much effort was incorporating for you? Would it be very difficult to close down the company again?
And how much do you pay for the accountant each month to take care about these things?
I’ve asked the MOL about freelancing:
Dear Sir or Madam, I hope this message finds you well. I am planning to move to Taiwan on an Employment Gold Card which includes an open work permit to my knowledge. From Taiwan, I would like to remotely work for an overseas company in Germany as a freelancer (or independent contractor). Do I need any special permission to start freelancing in Taiwan? Do I need to register as a freelancer first before I can start working? Do I need to have an official office address as a freelancer? Or can I just start freelancing once in Taiwan and declare all income at the end to the tax authorities? Looking forward to your response! Thank you!
This is the response I have received:
qwert_zuiop，您好!
有關您於109年8月22日致本部電子郵件，詢問在臺工作相關規範一案，為您說明如下:
一、依外國專業人才延攬及僱用法第4條及第8條規定略以，外國特定專業人才擬在我國從事本法所開放之專業工作，包含專門性或技術性工作、僑外資事業主管、學校教師、補習班教師、運動教練及運動員、藝術及演藝工作等6類工作，得無需透過雇主，逕向內政部申請核發具開放式個人工作許可、居留簽證、外僑居留證及重入國許可等4證合一之就業金卡。若您有申辦上之相關疑義，建請向內政部或國家發展委員會諮詢。
二、基上，倘您符合上開特定專業人才之相關規範，向內政部申請就業金卡後並經許可，即得在臺工作，惟從事工作之內容仍應與原許可範圍相符。至於擔任自由工作者承接境外公司案件是否須立案登記及相關所得申報等問題，因分涉經濟部及財政部等2單位之權責業務，建議逕洽上開單位詢問。
三、以上說明，如果您仍有疑義不明，您可再來信(函)洽詢。歡迎您多加利用！
感謝您的來信，祝您萬事如意!
勞動部 敬啟
Translation (using DeepL):
Hi qwert_zuiop, how are you?
I would like to explain the following information regarding your email to us on August 22, 2009, inquiring about the regulation of work in Taiwan:
According to the provisions of Article 4 and 8 of the Law on the Recruitment and Employment of Foreign Professionals, specific foreign professionals who wish to work in Taiwan in the professions prescribed by this law, including professional or technical jobs, overseas business directors, school teachers, tutorial teachers, athletic trainers and athletes, and artistic and performing arts jobs, may apply to the Ministry of the Interior directly through their employers for permission to work in the professions prescribed by this law without having to apply for permission to work in the professions prescribed by this law.The Employment Gold Card is a card that combines 4 certificates: permission, resident visa, alien resident permit and re-entry permit.If you have any questions regarding the application, please consult with the Ministry of the Interior or the National Development Commission.
2、Basically, if you meet the above-mentioned regulations for specific professionals, you will be allowed to work in Taiwan after applying for an employment golden card from the Ministry of the Interior and obtaining permission, but the contents of your work should still be consistent with the scope of the original permission.However, the content of the work should still be in accordance with the scope of the original permission. As to the question of whether or not a freelancer is required to file a case against an overseas company and declare the related income, it is recommended to contact the above-mentioned unit for inquiries since the case involves the authority and responsibility of the Ministry of Economic Affairs and the Ministry of Finance.
If you still have doubts about the above explanation, please contact us again.We welcome you to use it!
Thank you for your letter and we wish you all the best!
Ministry of Labour To Kai
Not sure what to make of this answer though 
I think they‘re telling me that I should ask the Ministry of Economic Affairs and the Ministry of Finance?
Attempt:
If your work is consistent with the type of work you can legally do according to the gold card, you can legally do it.
However, whether you have to do something with a company (MOEA) or how you declare taxes (MOF) is not within our remit to answer.
Okay, so I‘ll be contacting the MOEA next. Let‘s see what they will reply 
Also check with NHI.
Received a reply:
Dear Mr. Zuiop
Referring to your letter dated August 31, 2020, in which you inquired some information about being a freelancer in Taiwan. In answer to your inquiry for the article, we reply you as follows:
First of all, because you’ve already got the Employment Gold Card, we suggest you to contact the Ministry of Interior (the authority issued the Employment Gold Card) to make sure all of your questions will get the suitable answers. Please contact with Ms. Wengto discuss about the regulatory issues.
Besides, there are two kinds of organization in Taiwan: COMPANY and BUSINESS. If you want to be an independent contractor by yourself which not partnership, you can choose a limited company or a sole proprietorship depending on the scale and the business scope.
Following is the procedure for a foreign company/business setting-up in Taiwan (INVESTMENT COMMISSION, MOEA - Overseas Chinese & Foreign Investment):
- Apply for searching and reservation of company name and business scope.
- Apply for the foreign investment approval to the Investment Commission, MOEA, in accordance with The Statute for Investment by Foreign Nationals.
- Apply for the company/business registration.
In addition, there are many different ways to count the tax in the different situations, please contact with central competent authority (Ministry of Finance) to ask the details about the tax.
If you need any further company registration information, please call the phone number: 886-2-4121166. Thank you!
Sincerely,Dept. of Commerce, Ministry of Economic Affairs
That somehow sounds like I need to start a limited company or sole proprietorship first?!?
Hi! How did you end up doing this?
I’m currently in a similar position. I just got my ARC (spouse) and I just moved to Taiwan from Europe. I have been self employed 6+ years and I have clients in different places in the world which I provide services (programming & design related).
Currently looking at my options in terms of registering as self-employed because I would like to file invoices to my clients (companies and other self-employed people often abroad) and to receive the money directly on a Taiwanese bank for me to use here. With all the legal implications that would cause, which include paying taxes here.
From what I’m reading and what Taiwanese friends are telling me, the concept of a self-employed person does not legally exists in the same way it exists in other places. It seems that for me to work and invoice for such work, you have to register a company or sole-proprietorship. But also, they say it can take up to 6 months 
Did you end up incorporating a company @qwert_zuiop ? Was it a fast procedure?
I still haven’t really figured out whether self-employment (in IT) really “exists” in Taiwan or not. In addition, since coming here, I have experienced the bureaucracy when dealing with banks in Taiwan which is difficult to navigate without having either fluency in written Chinese or someone who speaks the local language and whom you trust 100%.
I did not want to have this dependency on someone who would basically be managing the company for me because I wouldn’t understand any of the documents I signed. In addition, I did not want to burden my customers with receiving invoices in Chinese and possibly trying to get back VAT from Taiwan. In addition, consensus seems to be that - given you don’t have any clients in Taiwan - incorporating in Taiwan does not bring any benefits compared to incorporating abroad.
So I decided against incorporating here in Taiwan and instead started a company in Estonia via their e-residency program. Total cost about €300 setup fee + €100 / month - all documents I signed electronically also were available in Eglish. The service provider for the Estonian company asked for my tax ID in and address Taiwan and made me confirm that I will be responsible for paying all local taxes and declaring the income I receive to the tax authorities at my place of residence. Otherwise, Estonian taxes will be levied on the income I pay to myself. The Estonian company now has a European VAT id which makes invoicing (within Europe) really easy.
I am not sure yet how exactly I will file taxes next year (the tax office gave me some generic information which documents I will need next year) saying that they will require “Certificates of Overseas Income Earned” stating “Renumerations derived from abroad for services rendered within the R.O.C. need to be combined and filed together with domestic income.”. The document goes on saying that these certificates can be either “documents verified by foreign legal tax authorities” or “documents verified by a foreign local CPA with a copy of the professional license of the practitioner or notary public”. At the moment, I am still not sure how exactly I am going to file taxes next year - guess I will see when time comes.
I registered with the NHI last month and now have to pay the minimum amount for self-payer. However, I am putting some money to the side in case they expect the roughly 6% of income after I file for taxes next year. Also haven’t really found out how that one works - will just see if they will contact me with an invoice after I file next year.
The Taipei Tax Bureau had a session today about filing taxes when on a Gold Card (although most of the points should apply regardless of visa type).
Some of their key points regarding this topic (from my memory):
On the other hand, overseas income (for AMT calculation):
According to the person present at the event, paying oneself no salary but only dividends from abroad would not occur any tax liability beyond the AMT in Taiwan, i.e. this would be acceptable “overseas income”.
Regarding the exchange rate, see: Exchange Rate when receiving income in a foreign currency? - #2 by qwert_zuiop
This is incredibly useful - thank you!!!
Useful summary. 
That’s all consistent with what I thought based on various tax guides I read last year and conversations with the tax office.
One minor point: Was it definitely 300 days here? I had it in my head that it was 330 days, but I don’t remember where I read it.
Not sure - I am quite certain it was a number >300 - but it could be 300 or 330.
Is this in writing anywhere official?
Tax season coming up and would like to have something in writing I can take with me to show them when they inevitably ask me to pay tax on my stock market profits.
Where would one find this? I tried searching before but found nothing.
There is this thread: Taiwanese capital gains taxes from trading on the stock market
But if you want an answer in writing, you probably need to ask either the tax bureau or a tax professional. They said one can just use their online contact form to ask (in English).
I was there too and thanks @qwert_zuiop for the summary. I only remember less than half of that 
Just adding on. The lady from the Tax Bureau confirmed that online filing (limited to the whole month of May, not earlier not later) is possible also for those who work for and receive a salary from an overseas employer. The total amount received in 2021 (gross, please take note) needs to be filed directly in NTD based on the official yearly rate published by the Tax Bureau. Finding this PDF table on the website seemed a bit tricky, but when the time comes I hope that Google Search will help 
The whole document was available on the English version of the website, but only in Chinese if I remember correctly.
Can you submit online if you are submitting together with your spouse? I remember years ago it wasn’t possible and I had to go down to the tax office. Hoping things have changed
Neither me nor anyone else that I recall asked about that during the session, I’m sorry. May is coming soon: by then you will be able to take a look at the online platform and check whether you can file together
It’s possible, but you still need to mail the supporting documentation in…in which case it might be easier to just go there (especially if your supporting documentation isn’t consistent with what they want, as in my case).
The link is here.
Correct, but it also depends on how helpful and knowledgeable your local tax office is. Mine is neither one nor the other one, so I would rather file online, send the documentation (whatever it is) via post to the central office and deal with them rather than receive wrong information, file wrongly or have to quarrel as usual.