Growbox is def a good idea, there's a lot of good info here about making it perfect.

As for sexing, I have vegged for a month last time and more than a month this time, and have yet to see preflowers until the second week of flowering... maybe its just my strain. It's said, however, that you should veg for as long as you see the preflowers (maturity), which will let the plant flower better (or something like that:stoned:lol)