Go with the 5 gallon. Research topping, bending, LST......everything you can read on it. I top my plants twice before putting them to flower. This gives me 4 main colas rather than one. I then tie down and train the 4 main stems through early flower to let other branches or off shoots come up in height to match the 4 mains for a nice even canopy. This keeps the plant much shorter and wider. Please remember that not every strain responds well to topping. Research the strain. With some strains your better off just bending them over, tie them down, and keep stress at a minimum. Good luck