i run perpetual cycles,so i veg thru the previous flower cycle.
my plants are usually about 1 1/2 feet tall when i switch em to flower and put em in super soil. and they are established in their roots. i like to keep them short and bushy, with lots of top nodes that are all an even canopy. then when i put em in flower i take off any veg growth below the half way point of the plant, so the top buds are really fat and dense.
usually i cut my clones small, only about 6 inches tall. and i top it once early, making about 4 main nodes... then after that ill do the 'oops i fucked up' method of topping on the top nodes about 5 weeks into veg to let the bottom nodes catch up with the top.
i also go from plastic red cups to 6" mesh pots to 3gal pots.. before putting them into 7gal pots of supersoil mix when switching to 12/12
the gdp needs to only be topped once, if you overtop it. itll stay too short in flower and get crowded out by other strains that are more agressive, but if done right itll be one of the most aggressive in the room, it just comes with time and experience, ive had the strain for a few years now so i know what she likes now.
other more sativa dominant strains need many topping and lst throughout veg and during flower (lst) as well.