They look good! If you want to scrog, now would be a good time to start. The idea of scrog is to "weave" your plant through the screen in the vegetative stage, and once the net is mostly full, switch to 12/12 so the whole screen is just a bunch of colas.
This diagram shows the structure of a proper Scrog
These plants have all been scrogged
If you just put a screen on top without weaving the plant through the screen, it's basically just structural support at that point, which might be what you're looking for but not a true scrog.
This diagram shows the common structure of cannabis plants under screens which have not been properly scrogged.
The following picture has a beautiful under current, but this is not a Scrog. Skeletal support at best, but again, not an example of a real Scrog.
One isn't necessarily better than the other, every training method will get great yields indoors as long as you create a wide, flat canopy with lots of bud sites.
For example if you topped your plants you could spread the two new main colas down and away from the middle to help spread the plant out. If you did that with 4 plants you could cover a lot of area. Bending over the tallest stems and securing them down is also what you probably want to do for the taller plants. The main goal of training is to keep all the colas at the same height, so it's a good idea to always be bending over any stems that get taller than the others.
If you don't want to top you can just use bending by itself (LST -
low stress training).
For example this plant is about a foot tall but is engulfed in fat buds.
Now take a look at the "guts" of this plant to see how this shape was achieved with LST
The main stem was first bent down and away from the center of the plant, towards the side. After that, the grower continued to bend the main stem in a circle around the plant. As a result, several lower growth tips rose up to become colas with fat chunky buds, giving much bigger yields than if there was just one main cola.
So you definitely have tons of choices as far as training! As far as when to switch to the flowering stage it's generally recommended to flip to 12/12 when the plant is about half the final desired size since most plants about double in size after the switch to 12/12. Hope that helps!