1. No co2 will not hurt small plants. Shoot for 1300-1500 ppms. You need to have a sealed room to gain the max effect of the co2 and that usually means you'll need an air conditioner to control temps. Exhaust will need to be on timer if you exhaust at all. I don't use co2 so I can't tell you exactly how to set it up.

2. Yes, I think you can very close to 2 lbs from that space.

Check out my sig for DIY projects and the OG GrowFaq for co2 advice.

Good Luck!