i do 12 at a time under the 400 in the veg room and i also keep mothers, the only thing with mothers is the size i just keep em in the corners turn an chop em down every now an then to keep em healthy an under control i also grow new ones every 2 harvests an flower the old mothers as they tend to get a little scraggly over time. you want your light a good 15 inches(this is for a metal halide, give or take a few inches) above your canopy anyways or else you will fry your plants, t5s work fine for veg i prefer a metal halide but thats just preference plenty of others use an love the t5's. if your looking for pure speed you can throw em strait into flower it wont hurt em but your yield will be small unless you have tons of the "lollipops" which people do grow that way, i actually accidentally threw my clones into flower this last time and had to wait for them to revert but now they are awesome! no topping neccesary. i personally prefer a good veg cycle but i have room for it. my yields depend on the strain but i get bare minimum 2 oz per plant an i usually grow kush which isnt a heavy yielder, if you want a heavy yield look into sour diesel or blue dream both of those yielded like crazy for me. hope this helps!