from my experience i would go with 8 (3") and give them more space when laying them out..
you will be kind of crowded with 12 (3") i think 5 (5") would be perfect but if there is no veg on them it could be a bit of a waste of space.
you could go supper crazy and use 2" net and put about 25 on there
its really personal preference luke.. but if it were me i would give a couple weeks of veg and use 5"
M_Jacobs you can still lollipop in 5" or any other, just make sure you trim all side growth when you flower to eliminate the popcorn...
lollies still take a while to trim