That is a great question. I re pot twice but this year I am re potting a 3rd time when I know the sex. The was using smaller pots and wasn't taking the effects of these small pots over the last few grows and it dawned on me they were never as vibrant as the ones I have in the big 5 gallon pot. The 2 gallons are obviously two small for max yield. Something else that is just killer this grow is the aggressive veg state - Make sure to keep the plants as close to the lights as possible prior re potting so they get max solar. I take the plants off their supports and set them on the ground after I put in the big 5 gallon (I think its 5 gallon - its obviously the right size - not overtly large but big enough for the roots to create dense, quality, and obvious higher yield. I am letting the plants veg a little longer this grow and its amazing to see who int the later stages the aggressive growth - amazing. The pleasures if growing. What a great hobby.
Oh the answer to your seedling question - the smallest bio degradable pet poss pots are good because you can stair step it into bigger pots without shocking the plant because you simply plant one pot into the other. I notice when i do this you can see the plant displaying a lot less stress features; sex showing early along with healthier green, minimal yellow and wanting to grow vs. forced to grow (exposing seedlings to plastic can't be a good way to start the genetic trek.) - by stair stepping you can control the conditons better -
BIODEGADABLE SHOT SIZED POTS. You can get them in bags of 20 for a couple bucks at Loews.