I'm was thinking the same thing!! I put all 7 of mine from Rapid Rooters, than 1 gallon smart pot and a final transplant to 5 gallon smart.... I feel like I'm in a jungle when I open my 4x4!
I'm going to try only 4 plants with the 5 gallons next run and scrog as well. But I would also like to set up a perpetual 4x4 with smaller quick yielding plants like my Fast & Vast. I feel like a bigger tent is in order and I would use my 4x4 as a tiered veg room.
Just seen you want to run hydro as well... oh man I'm afraid to mess with that stuff. I'm liking a more laid back approach to growing and hydro would not of allowed me to do that. I feel like I'm doing just fine in soil without having to check on a daily pH of water and such.