If you want variety you could do 4 plants in 2 gallons, maybe 3 gallons if you get the right shape to fit the tent and do 12/12 from seed. It will be tight but you can do it. The plants will stay small enough that light pen. won't be an issue. You can do minor defoliation if you get a real leafy/dinosaur leafed strain. If you top them before they start showing signs of flowering they can usually recover before flowering even under 12/12 from seed. I don't have much experience with growing slow growing indicas this way however. 99% of what I grow is hybrids.
Prolly get 1.5-2oz per plant with the right strain selection and a little luck. Pretty hard to get under 1.5 with a well fed plant IME.
What kind of light you using? 400 watt HPS/equivalent in quality LED's I think you could be quite happy with the results.