What are your lights?
What is your ventilation?

If you are grwoing an Indica strain you could be OK with 36 plants in 8" pots SOG.

If you are growing a Sativa, you could be ok with 2-4 plants in 5 gallon pots ScrOG method.

A 4x4 would give adequte breathing room for 4 plants if this is your first time. If you cram the growth in there without proper ventilation and knowing what you are doing you could run into a learning experience rather than a successful harvest.

Good luck and read read read.