Thinking of Upgrading from Cfl's to Hps. Heat related Question

I have a couple questions about the use of HPS grow lights.

Grow room: Upstairs closet. The portion of the closet that the plants grow in is approximately 3ft deep, 8ft wide and about 8 feet high. The other half of the closet is two elevated steps acting as stairs up to an attic door about 18inx18in.

I normally have an oscillating fan sitting on the elevated portion of the floor hitting all the plants in the room, but I also have a larger fan I use for hotter days. (The large fan is aimed at the wall at an angle, to circulate air around the plants.)

I keep the door of the grow room (which is right in front of the plants) cracked about 3 inches. Wide enough for air to get in/out but not wide enough for cats to get in.

The temps are regularly around 60-65 at night and 65-70 during the day. The grow room's gotten up to 75-80 but only on really hot days without the fan running.

Now...

I'm thinking of using a 400w HPS for this room and my main question is about the heat. Will running the fan in the room be enough to keep temperatures under control, given the ventilation of the closet? (Intake/exhaust through the closet or attic doors)

The other question revolves around the safety of the plants. Are HPS lights suitable for seedlings? Or would I be better off using a CFL in a desk lamp?

you're gonna need better ventilation than that for a 400W HPS. probably a decent 6" vent fan exhausting into the attic

you dont need the hps for seeds just use a couple of cfls till they get abit bigger, then switch to the 400,

also when i had my 400 it raised the rooms temp by about 11 oc without the fan on, only 5-6 with fan(inline sucking out)