Honestly I think your best bet for small bottom feeders is to stick with cories, they have loads of personality and don't take up much space or make a huge impact on bioload. There is also a wide variety to pick from.
As for your carpet plant... I have medium light with no CO2 and I decided on using Micro Sword (Lilaeopsis Mauritiana), it grows taller than DHG but should spread faster in medium lighting. The CO2 is a plus will definitely allow it to carpet more quickly than my setup.
What kind of look are you going for? Short lawn, tall grassy, thick, thin, etc.?