Hey bgray welcome to cann.com, yeah it is overwhelming at first, there's almost too much information about, but don't worry you'll soon get the hang of it.

A 600hps sounds about perfect for a 4x3 box, as for the intake and exhaust either way's good, so long as you which ever place you pick you can run your ducting easily to where you need it to exhaust from. (There's a couple of different ways you can run your ventilation i have mine set up like this, carbon filter---ducting---cooltube hps---ducting-----fan but) Just plan ahead how you wanna do it, you might wanna have the ducting height adjustable so you can move it with the light and suck the hot air right from under the reflector, just depends on your setup.

If you're concerned about $$$ i'd probably say you'd be best to go the soil route, if you go hydro not only is the system gonna cost a few $'s but your gonna need to buy some other stuff too like ph meters and ph adjusters, growing in soil is probably a little easier for the beginner too, problems in hydro can happen quickly wheras soil is more forgiving.

Good luck!