I’m wondering if 3-5 gal. pails would fit in a 2x4 tent, or if over crowded
Yes you can depending on how big you let them get and how you train them. I would LST and lollypop them and control the number of colas on each plant to maintain good lighting.
Autos or photos? It’s pushing the limits with either. Two would be ideal, but you’ll want to flip them quickly if photos as you will find it getting very crowded. I’ve got a photo right now that was flipped at 8 weeks and the canopy is well over 2 ft. wide, even with all of the training that I subjected her to.