Doing my first open pollination in a 2x4. Growing Swami Organic Seeds The One x Blue Moon Rocks. I’ve got 4 males in 1 gals and 3 females in 3 gals. I did 4 week veg and I’m up potting in fox farm soil. It’s been going well the gear is great. It was in the freezer for 3 years and all 15 seeds popped with great uniformity.
Yes, couple of gallons.
Depends on how big you want them but I’d suggest a min of 4 weeks if you want beefier plants but I’ve also flipped at 2 weeks in for smaller plant or full sativa or landrace runs where the plants WILL GET BIG if you let them veg 4-6 weeks.
Similar situation. Your plant size will be determined by your root mass. Smaller pots = smaller tap root = smaller root ball spread = smaller canopy.
If you have tall pots the tap root gets bigger and so will the plant but still will have limitations due to the amout of roots it can grow before getting root bound. ANother reason I love air-pots is the air root trimming allows for a plant to get bigger than if root bound; but this can also become a problem.
How many plants of those 15 are you carrying forward? IF ALL; I’d suggest going with 1 gallon nursery pots and just check their watering requirements daily. A minimum of 10-15 min should be given to check on things for any full tent if you don’t want fuckery so daily watering won’t be an issue this way.
In a 2x4 I just ran 18x solocups for a massive 18 strain f1 chuck. So 15 1 gallons could work if you train them straight upright and defoliate every few weeks.
Easy peasy in 16oz solo cups… but you’ll need to water daily the entire time… not fun when you’re having a bad day. 
Best of success @Beep !
Thanks dude. Great advice. I’ll want to run with as many as I can. I’ll get the 1 gals and probably do a two week veg.
I can fit 11, maybe 12, 1g pots into a 2x4 if I’m really trying.
For flowering I tend to max out at 6.
I water every 3 days or so.
Best of luck.