OK bro. 4x4 is a pretty decently sized room. I'm surprised no one said anything about not being able to fit 10 plants in there. Basically you'd have to grow 10 and pick out the males, but the thing is, what if most of them turn out to be female and you need to keep them? You'd have a grow room with too many girls to fit. I'd personally go with about 4-6 and use the 400W HPS. As for the HPS:

http://cgi.ebay.com/NEW-400-watt-HPS...QQcmdZViewItem

There you go bro.

Plus, isn't purple hash a sativa dominant plant GardenKnowm? So that means it can get a little tall. So goodluck homie and keep us posted with what you decide to do.