INSpectaDeck, here is a suggestion since you now have a 400watt hps. You should use that for flower, and in another location uses a few 26watt "GE daylight cfl's" for vegg. That way you can grow out clones/seeds/vegg plants with the daylight cfl's while you have your other plants flowering with the 400watt hps.

You could Vegg under hps if you wanted to , but the node space will be farther apart (aka streched out farther) then if you vegged under cfl's that are in the 6500k spectrum ( the GE daylight 100's) Remember with cfl's to keep the lights approx 3-6" from the plants that will make them grow nice and bushy.

If you use this method I suggested you will be able to harvest bud approx. every two month's. (when one crop is finished flowering , you grab the plants that you have in vegg and put them in flower, vegging more plants while the crop is flowering)

The Vegg chamber dont got ta be huge either if your just growing a couple plants n maybe a few clones a 2'lengthx1'widthx2.5'height
Grow box will be all you will need,You could use a cardboard box many people do just make sure you have proper ventilation. put four-six 26 watt "GE daylight 100" cfl's in there and you will have a great vegg box.