Personally, and this is just IMO

You're on track with the 400w HPS. In my first one or two grows i went the 400w HPS and loved it.
A 400 doesnt generate THAT much heat that it's a worry, but it's a good amount of watts for a closet.

Thats just my 2cents

Good luck! kick ass hobby you've chosen :dance:

Fingers :thumbsup: