I didn't see any pics of your LST. just your sprouts. I have been doing LST on my plants since week 2. As for letting the top go I have kept mine tied down as it grows along the outside edge of the buckets. Then LST the new branches as they grow keeping the canopy at a nice even 6" untill the cabinet is full horizotally. then I am letting them grow vertically till 12" to 16" high then induce flowering. my veg is 5 to 6 weeks.
I have 15 plants in a 4'x4' cabinet from seed and plan on growing 7 to 8 flowering trees.