Yeah, the reason why I want a sump is because I can have more plant's underneath the tank, and it gives me more water volume so that way I can play around more. I am sure I will have 10 honeycomb catfish. As for the hatchets, I know that they love to go carpet surfing. Are there any other top dwelling fish that would work? I was almost thinking WCMM because they are always on the top of my 20g. I also think I want a pair of rams, OR kribs, OR Apistogramma.
Having plants in the sump is actually a really cool idea. Go for it! The sump will be fine... even if it does waste some CO2, i think it would be worth it to have some emersed/submersed plants growing in your stand. CO2 refills aren't expensive...
And who ever said he's going to use pressurized CO2, anyway? I didn't read that anywhere.