I think if you are trying to grow “trees” a 5 gal will get you there. The biggest things to consider is how often you have to water and is there enough nutrients? If you mix nutes daily and water as needed 5 gal should work. You will just need to fill your plant battery back up more often.

if you want to keep it shorter start training them if you want vertical growth without training start topping , I’ve taken hedge trimmers and topped a foot off of mother plants before they come right back no problems… Not sure what country you’re in but if you’re in the US or it’s latitude I wouldn’t advise the latter those will be buds soon enough