5 gallon pots are not that high, like $2.50 at lowes. Highly recommend getting some. Clear out the other plants as the others said. I grow in an apartment as well. Definitely not easy or recommended. As for 4 ounces out of a 3 gallon pot, it can be done. Just not easy. A good heavy yielding strain helps. I grew some Bay 11, netted a bit over 4 in a 3 gallon, and a bit over 6 in a 5 gallon. Both in soil.