OP:

definitely look at IRO for a nice compromise between "stock" bikes and completely custom self-built bikes (tony at IRO will let you customize). i definitely think you sound like a candidate for an IRO.

in terms of size, no one can answer that question for you until they see you on the bike, but i can make an educated guess: you probably don't want to go bigger than a 57 or 58 for two reasons: 1) it's always easier to make a small bike bigger and 2) you want fixed-gear frames to be on the small side because it affords you a little more control (this is especially true of track bikes but it's true of fixed gears too). that said, like i said before--that's just an educated guess. no one can know for sure what size bike you should unless they measure you and preferably look at you on a bike.

good luck! fixies are awesome.