you could keep two plants in the 3x3 I think or use the 3x3 as a seedling / veg tent.
I think you are looking at probably something at least twice that size… but I tend to really want to give them more room than they need so that they can grow to their potential. I saw a couple of pretty good deals on grow tents on the walmart website the other day. Let me take a look over there and see what I can see for you.
got to walmarts website and copy paste this into the search field
Virtual Sun Reflective Mylar Hydroponic Plant 76x76x76 Grow Tent Box - VS7600-76
$179.99 and that would give you room to get around in the tent and still have plenty of room
Search: Grow tent on walmart for other options/ sizes.
I’m only growing one plant even though I could grow 12. I just don’t have the room for it. I’m going to increase that over the late spring and summer to a few more, but my thoughts are two or three plants in flower at all times.