, especially if any of your strains tend to the large side. You could do more if you want to try it, but you will need to be more careful about air flow through the canopy, and you may need to trim plants to keep them under control. Doable, but more hassle than having a bit of room.
Keep in mind that if you manage the grow reasonably well (this is AFN, home of expert advice, after all), you may end up with more than a pound of bud. Maybe you don't need more than 4 plants. If you want to play around with more, one way to do it (my go to for now) is to just fit in a few solos where you have a bit of space. It can work well in a 4x4.
Good luck with the grow.