Three quick questions for new grow box!

I am setting up a closet grow box that will be about 45" x 12" x 36". I plan on using MD and HPS lighting and will vent into the attic through about 1 foot of flex. I'll be growing Snow White in soil.

I have three questions that I could use some help with:

(1) How many plants are suitable for this size box and in what size containers (3 gallon)?
(2) What size MD & HPS bulbs are suitable for this size box?
(3) Should I buy fans now or wait to see how much heat is generated by the bulbs and then buy the appropriate sized fan, or does it not really matter because a timer will control the fans and regulate the temp? If it doesn't matter, what size fans are good for this sized box?

Thanks in advance for any suggestions. I have two seasons experience growing outside (1 plant last year and three this year), but this is my first attempt at indoor.

1. Being only 1 foot wide limits you to only one row of pots unless you use less than 6" pots, so 3 10" or 4 8" pots would be about it.
2. Maybe a 250w HPS or 2 150w? dunno about a 400w in that size box unless its cold there. what is a MD light? do you mean MH? I wouldn't bother with it and just use the HPS throughout.
3. Its about a 12 cubic foot box so going by the 3-5 times volume per minute for airflow, as stated in the FAQ, you'll want about 60cfm of exhaust. Shouldn't need an intake fan. You'll also want a fan in the box for circulation aswell as the exhaust fan and depending on the temps a fan blowing across the light or even a cooltube may be needed too.

The light and pots will take up about 2 foot and you'll be left with about 2ft for the plants so you might want to look into LST, topping or ScrOG as a means to control height.