I say go fixed gear. But you don't really need to decide on that. Not really. Well, maybe.

If you have a fixed gear, you can eliminate the rear brake. Maybe. If you are into that. I like no rear brake bc I do not have to worry about the brake set up of my chosen frame (disc, canti posts, caliper). I also do not need to worry about wheel size. As long as the big wheel fits in there a smaller wheel will also. Of course, if you go disc brake you can also be flexible as to wheel size.

I really like 26 and fixed. Mine are freaking bomb proof. Put a 36 hole rim on there and you can take pretty much any abuse offered. Only problem with this is that the front ring gets tight if you go too big, but I'm not like you. I like to spin.

The last is obvious, but make sure you have track drop outs. Since you are buying steel you can have the dropouts replaced for $100 if you are in any decent metro area. But you might not want to go there now. The redline mentioned above is a good candidate. If you dont have track drop outs look at the ENO eccentric hub. It's as kick-ass as anything out there.

Fork? I'm partial the the surly 1x1. Cantis and disc mounts. Run disc brake or canti brakes on any size wheel using Paul moto brakes.