These would be fairly small plants. No reason to use 5 gallons even with 2 in a 32"x32".
I'd consider doing 4 plants in 3gallons or 1 plant in a five-to-seven gallon. More plants = shorter vege phase... and you get a bit more risk-aversion with more plants, too. "1" bad plant doesn't ruin the whole grow.
2 or 3 result in weirdly shaped plants that can't take advantage of symmetrical growth. it will add inefficiency to the process and cost more per gram because of that.
heck, with four 16"x16" plants you can probably even go with 2gallons, if going soilless. stick to 3gal in soil, though. Consistently 75-100g plants only need about 3 weeks of vege, i'd bet, with soilless context growth rate. ~350g in ~12 weeks out of that tent. Any weak plant reduces that estimate, of course, but 4 clones could easily do that or exceed it with ~12 weeks.
AFter your grow, simply look at the root zone.. is it wildly wrapped around the outside restricting oxygen? If not, it was not too small. Are there large volumes of limited roots? If so, you can probably down-size. or, if lese severe observations, just fill the pot a bit more or less than you did etc... you can dial it in through observation.