I don't know that I can answer your question as you have asked it but maybe I can help you sort out the answers for yourself
when speaking in terms of increased yield id say the largest factor other than genetics is light
more light equals more yield up to a point...but more light also equals more heat control issues
as far as plant spacing.. you can fit as few or as many plants into a space as you want...
fewer plants equals more veg time to fill the space
for example
1000 watts of a 4x4 area
16 plants in a 4x4 area might only veg 1 week, maybe less
4 plants in a 4x4 area might veg 4 weeks
both will yield the same
i wouldn't want to transplant hydroton if i could help it
you could grow a plant in the 7" pot thatll fill a 2ftx 2ft area
but if your able to use a slightly large pot do it, theres no harm that's for sure
im not sure i got a full picture of your set up.. im wondering though would you be better off with net pots?
is this aero or flood and drain, or a top drip set up?... im just not getting a clear picture