You don't have to worry about a plant in a 5-gallon bucket getting rootbound. A pot that size will support anything you're growing indoors,
more than likely. The pot and it's size determine the shape and size of the plant. The roots tell the plant they have reached their limit of
growth and the plant quits trying to expand in size. If you want short squat plants use short squat pots. That's why you never see a huge
3-inch stem growing out of a solo cup. The plant knows it is in a tiny area and adjusts to fit the environment.
Also, I figure a 3-gallon pot will meet all the needs I have of a plant I'm keeping 3 months. A gallon a month after 2 months. Very few of my grows
go for even 3 months so I use a lot of 5-quart and 7-quart mini-pots. A 5-gallon bucket will cause you to waste time as the plant won't grow much
until the roots fill the bucket. You don't need nearly that big of a root ball and will waste weeks waiting for that inch-a-day growth you want. Next time
find something smaller for a final pot.
Good luck, BigSteve.