Im in my first run using this size tent (2x4). I’m running two 5 gallons right now in a SCROG….debating whether I can handle three five gallons in this space. My gut says 2 5-gallons or 3 3-gallons.
I'd do a single plant in a larger container for small tent then spread the canopy, but everyone has their own ways. SIPs with dry amendments is pretty damn easy.
Sub irrigated planters...they have earthboxes on sale for 39$ right now I saw on buildasoil. Pour water through a tube and bottom water, it's pretty low maintenance.