PLants look Great but I have a few questions

Second Try Grow,
Hey I got a Few questions.... Sorry no Camera I know it makes it hard
First off a little background....
I have 2 White Widow Plants 2 weeks old about, really green and they are kinda bushy I guess. They look good. Soil with no fertalizer. 3gal pots, They are about 3-4 inches tall.
I have a 400watt hps Lamp. I am using my walk in closet so I have only 3 to 4 feet of hight avialable. I have fox farm nutes, Big grow for Veg, and Big Bloom/Tiger Bloom for Flower......

1.)Hight, I would like to keep my plants at about 3 1/2 feet, do to my walk in closet. Do I need to top them off? How? When?

2.)When do I begin using my nutes? I have heard now which is 2 weeks in, I have heard 4 weeks in, I have heard never during veg only flower, whats the deal?

3.)When do I switch to Flowering? I know its about 6 weeks, but If i dont want my plants too tall do I start early, like 4 weeks in? or is that just what topping off will do for me?

Thank You Very Much.........

try bending and tying instead of chopping split the difference 3 weeks start with less than reccomended dose and slowly work up you can flower whenever you want your height limit as your guide your plants will about double total height during flower so if you want 4 ft plants flower at 2ft and so on i wouldnt flower under 18 inches