Here's a link to some directions on how to make a simple composter out of a garbage can, D.
http://www.uaex.edu/publicatio...
I think you could make it any size, and the key to good, quick composting without any smell or mess is to stir it up often, to keep it decomposing aerobically (with lots of air in the mix). If you let it sit too long, anaerobic decomp starts up and it will ferment and stink! You'll need to take a bag out with you for a while and find a source for some dry leaves, or grass clippings would work, too. Know anyone with a yard? Air, and a good mix of materials is the key.
If you don't want to go this route, then the worm bin is the next best thing. Worm castings would be an awesome additive for your potted plants.