1&2)You really shouldn't run less than 3000 lumens per sq. foot of grow space. A 400 watt HPS should run about 50,000 lumens, divided by 9 square feet gives you a little over 5000 so you're in the clear there. More important than how much light you buy is how much light is reaching the plant, so you may want to consider reflectors or side-lights to throw some light on the sides and lower branches.

3)For proper ventilation you'll want a fan that can circulate the air in your room more than once per minute. Assuming your room to be 6'x6'x8' you'll want a fan that can move more than 288 CFM, in addition to a standard oscillating fan to provide a make your babies bend a little and promote stem growth.

4)Carbon Filter is a must have, particularly with so little space between houses.

5)Buy a strong enough fan for your carbon filter that it can be the primary exhaust fan, and the only other fan you'll need will be the standard oscillating one.

6)Not an electrician, but my computer draws 750 watts so I feel like a 700 watt light and a fan shouldn't be pushing the limits of a single GFI outlet.

I've never tried an autoflower, but I'm given to understand that on the whole it will be a smaller plant. You may still find that 10 plants in a 4x4 space is rather tight. It can be done, but it requires a lot of shuffling and patience. If you use the bathroom I would consider dropping down to 6-8 plants or so to prevent overcrowding.

My inclination would be to put some sort of waterproof liner on the floor of the closet, set your table up in there, and walk the water in from the bathroom. At least it's a short walk =) First outdoor grow was nearly 3 acres from spigot to garden.