Hello ThreeKingsRP,

First off, IMHO, 600w HPS is good for abt 3'x3'.
For a 4'x4' area I would really go for the 1000w light.

You will find that a 600w light in a 4.5'x4.5' tent will get too hot if it is not cooled separately.

You can either have a separate fan/duct for the air cooled reflector plus your exhaust fan to exchange the air. Or you can use a exhaust fan from the air cooled hood and leave the other end open to draw air into the tent, thru the hood and then out. In either case the 270cfm fan maybe a little undersized for the job.

What about an air scrubber of some type? The odor will be substancial without it.

OM