ARC based on university / attending chinese classes

I am currently living in Europe.
I am planing to study chinese at a govement approved university.
I know to apply for an extendable 60 day visitor-visa and can stay in Taiwan up to 180 days with 2 extensions. My question now is, after 180 days can I change my visitor-visa to a resident-visa without leaving Taiwan ?? Having a resident-Visa, I need to have an ARC. In possesion of an ARC (due to attend chinese classes), am I allowed to work part-time ?? Or is it strictly prohibited ??

does anyone in here now how long it is possible to keep the resident-visa and the ARC ??
Do I have to make frequently extensions ??
I ask this, because I want to stay this way up to 3 years in Taiwan just learning the language.

I have a spouse (my girlfriend) and we don’t want to marry before I can speak chinese at a medium level (her parents support us as well, but give permission only, if my chinese is at an acceptable level for them). May sound strange for some people here, but most important it is ok for me / us …