I cannot answer most of your questions specifically. Up to a point, Taipei is pretty gay-friendly; or politely tolerant without being truly accepting. Also, not to put a fine point on it, Taiwanese are really friendly with foreigners (at least White foreigners). I think Taipei is a better place to be gay than Hong Kong or Tokyo (I don't know about SE Asia).

The Taipei gay community (really, communities) is large and most of it is pretty welcoming, though it can also be clique-y. With less flexibility than in the US, say, gay men identity themselves as either top or bottom (that's just a generalization, of course). It would be helpful if you knew Chinese, or at least were willing to spend time learning it.

My advice is a nutshell: take a 2-week vacation to Taipei and see how you like it. (Keep expectations realistic.)