Well the height I go is usually between 8 to 10 inches for a screen size of 24" by 48"
Veg time varies on what type of grow you have. Soil, Hempy, Hydroton, Aero but the idea is to train them into the screen and when the screen get about 75% full then flip to 12/12. Keep training them and fill the screen for two weeks then let them go.
Good luck man, you can check out my journals to see what Im talkin about.