It doesn't matter where you live to open an account with IB. We do not offer prop trading but could refer you to a group. if interested, send me a PM. you could trade the equity and future side from macau or HK without any problems. however, if you plan to actively trade FX, HK is one of the few places in the world where an FX license is required. We're in the process of deciding if it makes business sense to go that route.
Taxes: if you are american, it doesn't matter where you live. the only benefit is that your first 80K is tax free to the US.
visa: in our office over the years we've received approval for a number of visas. the criteria is basically that we couldn't find a local to fill a position. the positions we've filled are highly selective have fit the criteria. I don't think you'll find it that easy to fly into HK and hope to obtain a work visa. I have known some people who've done visa runs when their 3 month limit is approaching (visit macau, shenzen, etc) and return to get another 3 month tourist visa. I'm not sure how long you can get away with that but more importantly, i'm not sure if you'll be able to rent a flat, obtain a mobile phone, etc with a work visa. (it might be simple but i'd research many of the things you would often take for granted).
if you have other questions, let me know.