There are many different things to do for CO2. Well first you could just dose liquid ferts and see how that keeps you. For my 33 I will soon be setting up a DIY CO2 system with the soda bottles, the only thing I'm waiting for is the co2 diffuser. The only thing with that is that you have to keep up with making the new recipe every week, but shouldn't be too much of a problem since I do a water change every week anyway :)
I suggest buying plants off of ThatPetPlace.com, it's where I got most of my plants that didn't come from Petco. They have reasonable shipping prices and a very good variety of plants. Even the packages are fairly decent and the plants that you get in are in great shape. (If I had more money I'd be buying more plants from there lol)
You can search google for DIY Co2 systems or if you have the funds I would just look up a regular system and research exactly how to works and all the parts. The main parts are: diffuser/reactor, bubble counter, regulator and then the CO2 bottle itself. Hope this helps a bit!