Just to clarify, if your hub looks like this, you can thread a 16T or whatever size freewheel you want onto the freewheel side. Shimano, ACS, Origin8, White Industries, Box 2, and other companies make freewheels of various sizes. 16T is the smallest you can go with a thread-on style. BMX shops, both online and brick-and-mortar, often have a decent selection. You do tend to get what you pay for; the WI and Box 2 units I've purchased have lasted forever. The others not so much.
As for bars, I think track bars are horrible for street riding. Get a road bar of some kind instead, and consider putting brake levers on it so you have a "hoods" hand position that makes climbing a lot more fun. And brakes are always a good idea, at least on the front wheel.