You can buy any 1 1/8 inch threadless fork, but you can't use any old headset. it has to be an integrated headset, (hence the integrated headtube). You will need cranks with a euro bottom bracket, and you will need to run a 14mm axel in the rear. Thats just the basic stuff that you can figure out by the frame specs. ither then those few nessesarry things you can pretty much do what ever, you don't have to worry about your rear brake and chain clearance because you have seat stay mounts so you can run as small a gearing as you want. Remember though, the smaller sprocket you put up front, the smaller driver you have to put in the back. If you have the money your best bet is to buy a cassette hub. They can accept a smaller gear and they are usually stronger and more reliable depending on which one you decide to go with. I dont have much experience with cassettes though but there are a few people on here that could give you some advice on which one is good to go with .As for other things like bars, rims, tires, whether you want to run a gyro or not. it depends on what kind or riding you will be doing but alot of it is just personal preference.