a passive intake is a hole.

a 265 cfm fan is just a normal fan that moves 265 cubic feet per min.
no pics needed man

it is hard to say if you'll need to have your lights on at night
you wont need it if you have a proper fan.

and a small heater with a thermostat isn't much money. it'll keep it warm if the temp drops

I have never heard of a ballast that can take both kinds. are you sure you arn't getting a HPS ballast and a conversion bulb?