CO2 gases off even if you stir the water too much. A sump is a bad idea to keep IMO. Go with the canister and insert a DYI reactor out of a household water filter.
Make that two canisters.
MH is too much. The tank height is the key ingredient. I made myself a nice carpet out of Ranunculus Inundatus. You can use almost any small plant to carpet the substrate. The MH creates more problems for the beginner and you could end up being frustrated by algae.
If you do a plantless cycling don't turn the light on until the tank is stable. Otherwise, fill it with plants and start the CO2 right from the start. Keep the photoperiod and CO2 low at start and increase it during the next month after the tank is stable.