In my experience, I've been able to grow some ferns, mosses, and some crypts with a sponge filter with an air stone inside. The 10 gallon shrimp tank had 20 watts of screw in CFL with no reflectors. I didn't do water changes and fed the shrimp daily. I don't really know if they decrease CO2 levels. I was always under the impression that there is some CO2 diffusion through air in the pump, but it may not be enough to offset the loss from surface agitation.

With such little light the ground cover plants such as glosso may tend to grow up, but you should give it a try. I know when I first got into the hobby I thought I needed 3+ watts of light on every tank I did, but I soon found out that more light generally leads to more problems.

I have a 30 gallon with a 2 X 55 watt bright kit from AH Supply. I wish I would have gone with something more along the 75-85 watts, because sometimes I neglect the tank and it gets a little crazy. It really depends on what you try to do with the tank. Everyone has their own tastes, goals, ect.

Did the people at the pet store sell you a "Brazilian Sword plant"? If that's the same plant I don't think you will able to grow it submersed , but I could be wrong. I bought one for my first tank and it quickly melted .

Might I also suggest on other thing? If you can at all help it buy or trade plants from other hobbyist. Aquatic Plant Central has a great sale/trade thread with tons of good stuff. Usually you will get much better quality stuff from other hobbyist than the pet stores or mail order retailers.

Good luck & if you need any plants feel free to shoot me a PM and I'll try to mail you some plants. I don't have a very wide selection but I may have something you could be interested in.

Have Fun,
Creighton