I've seen great growers doing 4 lettuce, bok choy, or kale per 5 gallon bucket. 6 gallons is one more gallon!

I'm doing 3 choy in one bucket myself. We'll see.

I've grown 7 swiss chard in one 5 gal before with no real issues but it was really crowded even though chard is upright growing. The next time I did it I cut it down to three. 3 or 4 of anything you mentioned is fine. It'll be tight but not too bad. Biggest thing is you don't want it so packed in that you stop any airflow around and through the plants. Leafy greens hold a lot of moisture and when packed in really tight with no airflow can be susceptible to powdery mildew on the leaves when humid.

Ask yourself not only how many can I fit but how many do I need. Since you can harvest the outside larger leaves on those plants and continue to let them grow, and they grow fast, you may need less than you can pack in there and give the plants some more room.

I was leaning towards a minimum of 2, but wondering about 3 or 4 in each. Im thinking i will go with 3 each.