First time mainline ?

You need to let the plant recover and get some vigor going before you flip to flower. I'd let everything grow out atleast 6in to a ft from where it is now without you stressing it. That plant is super stressed and has barely any leaves if you flipped it to flower any time soon then it will only grow a couple nodes durring the strech if that.

mainlining is fine, but instead of stripping the leaves with the branches, leave the leaves in future-- even if it isn't what the so-called 'technique' calls for. LEaves power growth. It's one thing to remove axilla, but gauranteed net-negative to remove all those leaves. The pattern of growth you shape matters too.. you ahve an empty cetral area and colas that are really close together in a circle. This doesn't effectively using the space. Yes, it will stretch just like normal. Nothing different there. More colalas oes not meean more yield. After a point all you are doing is overcrowding the area and will get a higher percentage of larfy buds due to competition for light. Yield is mostly dictated by DLI (daily light integral) and canopy size. Training does help decrease proportion of larfy buds. Energy is the currency for yield. If it doesn't absorb more, it doesn't yield more. The size of canopy limits how much it can absorb. ~3 colas per sq ft is about all you need. work backward from that in future. Train resulting colas from your mainline to fill in the space systematically as best you can. A scrog can help with this and provide support - not all plants need it, but impossible to predict 100% which will. don't get caught up in esoteric 'techniques'. Mainlining mainly just add unnecessary vege time and wastes your money getting to the same canopy as you an achieve through similar means that don't involve pruning off so much wasted growth and resources. Stripping leaves as part of instructions is a big giveaway that it's "bro-science," too. don't worry about the labels. Do whatever it takes to reach a targeted canopy with the least amount of vege time needed to get there... no matter what 'they' label it.. it's just manipulating apical dominance. All these things have been done for centuries with other plants. None of it is new.

I know mainlining as two main stems off one root base. this is 4 main stems. So its not technically mainlining but similar to it. And it looks good. Just chop that one branch all the way back that snapped off and be gentle with them as it looks like a lot of them are spitting. Very easy to crack the trunk in 2 if not being gentle. Let it grow out a bit as well, no need to lollipop it just yet. SCROG net will help in the comming days/weeks.

Veg, think of it like constructing the frame work. Buds can only grow on future frame, for now just let her grow. I just find it's never worth the stress to top, top and top, you can literally just let her grow vertically for 5 weeks and bend her over to the ground, this breaks apical dominance and will give you the 16 stems without the 5 weeks of stress recovery. 5 or so weeks of growth, with a 2 week plant (in terms of mass). Good luck.