ur in luck...I just finished battling something similar to this. Check out my sig and take a look at my photo album. You will see that my space isnt much different then yours and I too have a head room restriction of about 3.5 feet. The problem will be with you being greedy just like I was. About 4 plants would be all that I would recogmend. If you crowd out the space the plants will become over grown and your issue will be light penetration. If you crowd the space the plants will fill in the light space and then begin to compete for light. Stretching occurs and if you dont prune or thin then you get too much vegetation not getting light lower down on the plant. Bottom line, make sure you have about 24" off center from the center of the pots spacing. Even that may not be sufficient.