The only thing you have to remember is oxygen is good for the roots but bad for the plants you'd have to exhaust all that O2 from the plants so the CO2 can absorb through the plant. Just get a bottle of oxygen from welding supply store and put a CO2 controller on it probably save you some money...
Well if u leave it in your room for 5 or 6 months that thing is gonna be huge if u know what you are doing. Secondly what kind of lamp u gonna buy with 20 bucks I'm guessing cfls