Veg them at 500 with your light 2-3ft away.. then flip to 1k and bring it down to 18-ish inches when you flip to 12/12... if you notice your top leaves doing funky things.. try moving the light up.. or bump the wattage down to 750.. You just need to get used to your light.. in your grow room.. that will come with time!

Depending on the strain and how big you let them get in veg.. you could put anywhere from 1 to 16 plants under that light.. its all in how you grow it!.. I would say 10-12 would be a safe bet, and flip when they are about a foot tall.. or you could veg 1 plant for 30-45 days and have a nice tree in your closet.. lol.. I would personally stick with the first option.. good luck!