Not sure how reliable of a reference this is, but it appears to be a decent introductory piece by first glance...
http://www.growweedeasy.com/germinate . I would suggest reading this, as I anticipate you may have planted your seedling upside down. At this point I would leave them alone, but just for future reference.
Regarding your 'main question', I'm not sure that we know that for sure either. When it comes to plants, some species/strains are sensitive to light during germination, which will inhibit growth; some don't mind either way; and some benefit. I've always gone by the rule that you should keep them in the dark until the sprout breaks the surface. However, if you've planted correctly (about first knuckle deep o/ 2.5-3 cm's), it shouldn't matter much. It's more important to have a warm, humid environment.
I used to go by the rule that each plant should get about 100W, but we're finding that 75W may be more sufficient. I would recommend a 400W Metal Halide for vegetation, and wait to flip them for about 3 weeks, unless they grow like crazy. I anticipate that they won't, this being your first grow (no offense). Then switch them over to a 400W HPS for flowering. I think a 400W light is appropriate for your first grow, as well as the number of plants. Save money, dial in your skills, sell it in a year, and buy 1000W's from there. Remember that as they get larger, space between plants is important.
Any other Q's?
Btw, Jorge Cervantes, The Weed Bible is a priceless reference for a grower. It's prob $20-30, but well worth it!