As a fellow big guy(6'7" 270) I can tell you this: Cheap wheels make life difficult. I have ****ty wheels, and they cause more problems than anything else. You can probably ride the typical L/XL frame without issue, but wheels are going to be the problem spot. And good wheels are expensive(I was quoted 400 for a basic set of decent, hand built wheels).

Other than that, find a bike you're comfortable on and ride it. You'll find things that work and don't work for you and either modify or replace them. Fenders and lights are pretty much the only things I consider essential.