Thx mate was gonna use Metal hailed bulbs for veg I heard with Sutch low power and using a cool tube I heard u can get them down 12 inches above plants don't know about seedlings tho was gonna use a t5 striplight for them say about 4 to 6 inches away
Yeah with cooltubes you can get much closer, the down side is the closer you get them the less area they cover. Roughly speaking a 250w is good for maybe 2.5ftx2.5ft. I would not fill your space completely, leave 10cm around your plants to the walls. Your better growing slightly smaller canopy and having it illuminated properly than stretching your light thin over more canopy.
I'm sure after a grow or two you will have it dialled in and know what is best use of your space.
Once your rolling in bud and money you can always change those lights to 315w CMH.
Edit, for seedlings any sort of florescent will do, t5, cfl, whatever.