Train the main stem through the screen and then tie it down and if and when it pops back threw you do it again. The bad thing about using seeds is if you get some males you will have to rip them out of the screen, which can be a real pain. In that space I would use 2 at most. Try to get a mother plant that you can get some guarantied females from and that will be your best bet IMO. As far as veg time goes, you should go 6 to 8 weeks in order to fill the screen up. Look up Justaseeds thread "lovely Ladies" it is a very detailed thread on scrogging. If you do it right you can get a nice little harvest, 2 to 4 OZ's if you can get it down, but that is extremely good results.
Adieu