I grow 3 in the same size space in 3 gallon pots, I wouldn't try 4, it will not be enough. 2 is comfortable, 3 is a squeeze, 4 would be a nightmare. I do grow them at different stages though, so plant 1, wait 3 weeks plant another, wait three weeks, plant the final seed then continue the cycle as long as you like. Doing it this way, you only really get 1 at full size all the time, the other two are usually coming into stretch or still a seedling whilst the third is in flower and large.