New grow room questions: w/pics

[noober]

This is my ballast, appears to be HPS and I will be growing in soil.
2) What kind of bulb(s) should I buy? Should I get one for early stages and another for flowering? Should I get any conversion bulbs?

This is the hood I have which will go in this tent.

3) The hood measures roughly 20" wide by 24" long. How many plants can I grow in there?

 

[PitViper]

use a 400wMH lamp for veg and change to HPS lamp in bloom....4 small plants

 

[noober]

Thanks. any recs on a decent bulb that won't break the bank? I' ve done a little searching and some seem to think that using a MH for veg isn't that important. thoughts? BTW all this stuff was donated to me by a family member so thats why I don't know a ton about it. I'm reading as much as I can (book and web) but it's a lot to take in and I really appreciate the help.

When in comes to air circulation; is household air considered fresh air? Meaning if I pull air in the tent from a bedroom is that sufficient or should it be from outside? I'm still debating using an attic or a spare bedroom.