You can't really have a lush garden of a tank with low lighting. Certainly not anything like some of the beautiful tanks you see on this forum. It is possible however to have a very nice looking tank if you stick to low-light plants that will work for you like java moss, java fern anubias etc. You must also remember that your plants will grow rather slowly, don't expect too much too soon. Plant placement is also very important, I have nothing planted in the ends of the tank, there's just not enough light. Instead I filled these areas up with driftwood and my fish seem to really enjoy these dark areas.
CO2 is generally used with higher lighting levels, I'm not sure it would help with a low light setup. It may even cause problems. Perhaps someone with more knowledge about CO2 could comment on that.