you're welcome.. i hope it works out for you. i will say this.. your plants don't appear to me to be showing signs of stress yet.. so that's a very good thing.. your plants look great!
a great way to thicken up the stems and branches is to put an oscillating fan on them. though it will cause vert growth to stall a bit, you'll notice the main stem bulking in a couple of days. it's a natural reaction to wind in nature. (don't use a stationary fan.. it just beats them up and causes wind stress.. for some reason that little break from the wind makes a big diff.)
about when to flower
those plants? imo, after you've successfully labeled and taken clones.
other than that, anytime after 6wks to force flower/sexing.
other than that, because of the new shape the topped ones are going to take, i would pinch the tops of the short ones too. otherwise, you'll have some that grow straight up, and the others out and up.