Hey Z,
1) Yes in my opinion it will be sufficient for the space. The lumii ballast is working well for me, although i haven't had it long.
2) Check out the cooltube, with ducting and an exhaust fan it really does a fantastic job at controlling the heat. It is far superior to any open bulb type fixture in terms of heat regulation.
3) I would steer clear of dual spectrum bulbs, rather get a specific MH/HPS bulb and change them accordingly.
4) Even just as a hobby, it get's pretty pricey to put together a proper grow setup. Other considerations would be humidity/air movement (oscillating fans), intake fans etc.