I thought it would be a good idea to put plants in now. First it will give them chance to get established before they get mauled by plant eating fish and secondly whilst cycling any plant material will breakdown and rot producing ammonia hence driving the cycle as more food for bacteria to use.
I am by no means an expert, I'm not even a beginner yet. I have been looking after a small 10 Gal tank, but recently I have upsized to a 38Gal tank. I am in the same position as a lot of you guys. Just got set-up and at the start of cycling.
When putting in the plants make sure they have a good root system, preferably they should be rooted in a little pot with rockwool. it's worth paying more of these properly rooted system, they look better (healthier) and in the long run last longer.
As for using Carbon Dioxide, how would you use it? i have seen Co2 aeration used in tomato hydroponic setups before, but would introducing co2 into the water defeat the purpose of aeration?
Best thing for plants is good lighting (full spectrum if poss) and the right food, with this ya cani go wrong.