You got the light!!!!
Awesome... You will be happy with the HPS...
Just remember, if your temps get out of control... you can always slap that bulb in a cool tube and get rid of 90% of it's heat!!!
Congratulations...!!!
As for the ventilation... that stuff is pretty important...
Just as in the light, my suggestion is to get a little bigger than you need... that way you will not have to upgrade next week...
Passive intakes should be adequate, but I would deff. put a strong cage or centrifugal fan on the exhaust...
You can put the fans outside of your grow space, connected with ducting... just make sure that the intake cannot bring in the exhausted hot air...