dude, first you need about 1 gallon of dirt per foot of plant....light requirements for veg is 18 to 24 hrs a day...if I were you I would go 12-12 when your 6 inches high, dont top it ...you dont have enough light to reach the bottom leaves...going through that myself right now....if you flower(12-12) at 6 inches, the plant will finish at about 1 and a half feet...you should get a nice big top bud that way....and keepyour girl about a foot from the light or that hps will burn your leaves....luck to ya