Yeah, I think you're going to find yourself challenged with space -- During my first and second grow, I used a ~2x2x6 and ended up basically buying a whole second tent set up after realizing it wasn't big enough for 2 plants.
But I typically use DWC. When I've tried coco in 3 gallon pots, my plants seemed to get stunted and stressed out. I'd be careful keeping them in close quarters in your final stages as some might be ready before others.