Are you using the Fluval system?
For plants, anything thats fast growing will take advantage of the CO2, i assume your tank is using the flora substrate which is enriched with nutrients so carbon is your primary bottleneck nutrient.
Almost all plants will benefit from CO2 so any plant you want will be fine. Just note that if you have slow growing plants you should probably inject less CO2. If your lights are strong enough, I would recommend HC as it is a beautiful carpeting plant. It reacts very favorably to CO2 and pearls often, creating a stream of bubbles that rise up from its leaves.
CO2 is highly dependent on what plants you have and what kind of lights you have. HC is a very high light high carbon plant, so CO2 is needed to help it grow. If you use plants such as anubias, CO2 is useless because the plant wont take full advantage of all the carbon being pumped into the tank. Any fast growing plant would be good for a CO2 injected tank.
For reference, I run a 5g with 1 CPD and 1 Oto, I pump 1bps of CO2 to sustain 2 6700k t5 bulbs (non-HO) for dwarf sag and HC carpet. Anymore than 1bps, my CO2 saturation goes too high and my fish start to asphyxiate. Any less and its not enough for my plants to pearl. Your tank seems overpopulated so you might want to keep a careful eye on your co2 and fish health. Finding the balance is a bit tedious but worth it in the end.