When it takes up roughly half the area, you should have enough growth after flip to fill it out.
Scrogs are great for systematically distributing growth. Use it to train the plant out horizontally until half the squares area filled (not with a branch but with canopy coverage). Then, let it grow vertically which is also when you flip to flower. prune off axillary growth below the scrog, but keep the leaves unless it causes congestion.
You probably want to use the scrog a bit sooner in future. Easier to keep something bent down as opposed to trying to bend that dominant branch down 4-6" under the scrog. As long as it's still bendable, it shouldn't be a problem. The branches do become more rigid with age (of that branch, not applied to new growth, obviously).
As far as how many primary colas to grow vertically.. i'd shoot for 3 colas per sq ft. More will not increase yield. It'll just distribute same yield into smaller buds.
Best method? top, lst, doesn't matter if efficient and systematic about it. I prefer topping because i can more precisely posistion branches and where they will grow out etc... IF it all comes from a 'spine' of LST, then some branches have to grow a lot longer than others despite having roughly he same vege time to grow. So something is going to be short or over-grown and that means pruning off more wasted growth to avoid congestion or to comensate for different length primary branches. 'something' has to reach the sides and corners, right?
If you want to save time/electricity, go with more plants. This will shortend vege time required to fill the space. Still same guidelines.. fill half, flip to vege.
You have ~4 weeks of strong vege growth after flip to flower. Depending on your local growth rate, you may want to flip sooner or later relative to 50% of the area filled. This takes a little trial and error and depends heavily on your local variables. Slower growing may want to get to ~2/3rds filled then flip.. train the rest of the horizontal space and let it go vertiaclly... faster growth may require more training after flip to flower. Then, you got genetic diversity, lol...
So, the rules are more guidelines. Adapt to reality above all else.
symmetcial plants and square spaces are easy to train than oblong or asymmetrical plants. Can't always do that, though. e.g. if you do two plants it's going to be rectangular in shape instead of square.
Have a goal for the canopy... work backward from there to devise a plan to reach that goal in the most effective way with the least amount of wasted growth. it may take a couple cycles to have the familiarity to do it well. Even so, it's difficult to guess which plants are big stretchers and which are not. mitigate big stretchers by continuing horizontal training deeper into flower than a plant that doesn't stretch as much.
Keep that canopy even.... understand how to manipulate apical dominance... easy-peasy.