Hi,
One square foot should be good. You def want them to just touch, not overlap but use all available space. Aero is good fast growth and you will want to prune the lower braches that won't get much light anyway. I always go by 1 sq ft per 1.5 foot vertical height. That is with areo and pruning. If you plan to top and grow bushes then maybe make a little more room. Did you build the system? Would love some pics.....good luck, PEaCe