I knock jack about fitting a bike to be honest, especially for someone with your height. What I can tell you is that you will be ok on the aluminum frame, I am over 350 myself closer to 400 actually and the aluminum frame mt bike I recently bought is holding up just fine. I might recommend a mt bike to start for you they are more durable built almost like a tank on 2 wheels. I have a 29ner wheel size and love it. As for how a frame will fit you- that I have no clue. Bigger frames will cost more- just like most everything bigger will, maybe just save up for it?