If you are on JFRV, article 48 sub-paragraph 2 of the Employment Services Act applies to you and you hence to do not need to apply for a work permit. Article 48, ESA
You could set up a Co., Ltd. (有限公司）and be the general manager (負責人). Taxes would be levied on company profits.
I'm sure there are many posts similar to yours on Forumosa. I would suggest you use the search function.