Thanks for the info, it definitely helps. Ok, at 1.2 cubic meters, I would definitely suggest an air cooled HOOD for your light, not an air cooled ballast.
As for keeping your door open, during the veg stage, its fine. And truthfully when the lights are on during flower its ok to have the door open too. The only thing with leaving the door open during flowering is whether or not you will remember to close it before lights out.
If you leave the door open I would not suggest adding CO2. All the extra CO2 would be lost right out of the open door. You are growing in a pretty small space with a pretty decent air flow, and I do not think adding CO2 would make all that much difference, but I would also say it couldn't hurt.
Another thing to remember, given your space is that you are working with a Sativa dominant strain. It will most likely have a tendency to stretch a good deal once the flowering cycle is started (I have not worked with this strain and do not know exactly how much stretch to expect). So keeping an eye on plant height will be rather improtant; you do not want the plantsgrowing right into the light.
Just some things to think about. I would also suggest investing in a good grow book. I would suggest Jorge Cervantes' book, its simple to understand and covers just about any issue you may experience. Best of luck to you. I got a seat here and will be real interested in seeing how this one goes.
