Very nice job on the grow so far NateRR!! I love growing OG's, there so much fun, develop beautiful flowers and really stink so good!! That LST is really bushing your girls out well...I would suggest continuing to do that as much as you have room for before you install your scrog screen...will really help later fill that screen up fast!! You should be fine with the 400w MH, but when it come's to flowering time, you might want to pick up a 400w HPS bulb.... will help give the ladies more of the red spectrum which seems to be better off in flowering, but MH can also be used.
Can't wait to see how these start really filling out as they get closer to flower...
Great job!