I'll wade in, so I like smaller plants, don't need volume. I have a 2x2 in it I would only put 1 plant to maturity if your tent has a  low ceiling your going to want to almost run it from seed as flower ie 12/12 just to be sure your not bumping light by the end. Using a screen of sorts you can train it to fill the space, use a short stature plant, use it to start plants to go outside.

you'll never fit a 5 gallon bucket with growing plant in it unless you have headroom. see photo of my 2x2 with 2 3.5 gallon buckets. don't disregard lowboy style tubs. roots in water are like cats in containers, they will be fine.👍

others here will have wiser and more clear ideas. we have a lot of experience here to help.