Just to answer a few more questions you have. Mylar is good yes white paint is better because it reflects more evenly. Not an option for everyone. The MH for vegetative is ideal. Most use CLF's because their cheaper to run and obviously less heat. Yes the ballast should be external.

As for Co2 there are tablets you can dissolve in water. They work and the plants will grow incredibly fast just a small mention I don't have much advice on Co2 systems because I don't grow alot of plants but they are very inexpensive to buy and will supplement for a proper system while you think it over. Do a search for No Mercy Co2 Tablets. And check this thread http://boards.cannabis.com/showthread.php?t=54651 You could use the basic concept and apply it to your situation.