Taiwan visa for Brazilian (Taipei)

Hi anybody can advise me? I am Brazilian passport holder and at the moment I am in China for study. My Indonesian fiance will work in Taiwan for 3 months only, and I like to stay with her in Taiwan during she works there. We both will need to enter Taiwan on September 10. However actually we will get married on Sept 5. So, means when we apply visa to enter Taiwan our status still single not married yet. My question is:
If my first visa application is Regular Visitor Visa for 30 days only, once I am in Taiwan can I extend my visa to another 90 days by my wife personal sponsorship letter? She has a very good contract agreement with the big company in Taiwan, so actually for the financial guarantee for both of us to stay in Taiwan during her contract will be no problem. Please if somebody from this forum can give me the advise on this.

And anybody can advise me how much the minimum bank statement I should have for Regular Visitor Visa 30 days application?