Welcome to Forumosa; Welcome Back to Taiwan.
I currently run a Branch Office & have looked into these kind of things.
Given your goal is to get an ARC and do so with minimal expense and (currently) income, a branch office may not be the best structure for you. To set up a branch office that can hire you, you will have to make an capital investment of around 500,000 TWD. The branch office should make yearly revenue of more than 3,000,000 TWD in order to retain the ability to hire you.
It is possible to set up a company without a CPA, and in recent years the government has put effort into English-language websites that explain the process. Using a CPA will typically cost you 20k-30k TWD for the initial setup, and then their monthly fees.
One new visa that you may not have heard about yet is the Employment Gold Card. It’s an ARC with open work permit that you can apply for directly, online, without sponsorship from any company. If you qualify, it could take away the association between a corporate structure and your ability to reside in Taiwan. There’s an extensive thread.