I'd say gearing depends on how you ride/how strong you are, but start off low, it's better on your knees and you develop better spin. I'm a relative newbie and I run 44x18, which I am only now thinking of bumping up. To find your starting gear, look at what you like to use on your road bike, and then maybe drop it down a tooth or two, as you'll have to use it for stopping and starting, in addition to just riding.
Converting can be a PIA if you don't have any tools. I got fed up trying to get everything together to do a conversion and found something cheap on ebay. Now, I'm ready to actually do a conversion, but I'm glad I didn't just keep waiting. Converting's a great learning experience, but riding's waaaaaaay more fun.
Or you might want to keep scouring FOR SALE ads/Craigslist/whatever for a good deal on a used track bike: IRO, Fuji, Bianchi, Surly are all reputable brands.