I would LST if I were you. Big benefit for very little effort. As for topping...some strains like it, some don't. It's all up to you.

There are a few products out there that claim to be just for this. However I've never used them. I'd stick to the tried and true if I were you though. You can switch the light cycle to 12/12 whenever your ready and play the waiting game for sex, like I assume you did with your last grow. Or, you can take a cutting off of each plant once they are big enough, root the cutting, and sex it with a 12/12 light cycle. If you had your clones and "mothers" marked, then you'll know their sex without bringing them out of veg.