General questions regarding transition to the Flowering stage

Good afternoon, fellow growers

It's my first grow and now I'm at the point where I need your help regarding Flowering stage (it's been 16 days since I set light to flower). Pictures of my grow in the attachment.

Brief info: My grow tent is 80cm x 80cm x 180cm. My light is "Vipar Spectra LED V900". I have 4 hybrid plants (2 hybrids are in 20L pots, which are my main plants and 2 hybrids in 4 L pots, which are just reserve/test plants). During veg stage I've been doing SCROG along with LST, Topping and Lollypopping. Here are my urgent questions regarding Flowering stage:

• Do I keep doing SCROG method while in the flowering stage or I leave it the way it is after transition from the veg stage?
• Do I need to move the screen higher while my plants grow higher in the Flowering stage or I leave it at the same "10 inch from the plants'" base level that i've been keeping?
• Am I allowed to prune the plants in the flowering stage? I've read that it's allowed only in the first 14 days of flowering then the plants aren't allowed to be touched. However, my plants are 16 days away from Veg stage. I'm asking because some of them are really crowded now and some are below the screen and don't get the light.
• Some of the leaves' tips turned yellow. Why did that happen?
• A few leaves turned completely dry and brown-yellow. Why did that happen? Is it because they didn't get the light and died?
• The last question. Do I need to do anything except watering during flowering stage? I feel like main work and training has to be done in Veg and in Flowering it's just about water, light and air.

My apologies for posting that long question. I tried to keep straight to the point.

Thank you!

I don't see a scrog screen under that canopy, maybe it's just covered by plant material but if you removed it already just leave it off. You are supposed to leave the screen throughout flowering phase and take it down after harvest but it's your grow do what works best for you. You don't have to move the screen once in place; grow the plants out and weave the branches into it for an even canopy. It can be difficult to get to your plants under a screen to water and whatnot....if you took it off though it's fine just do without it your canopy is filled in already just go with it as is. Could be a challenge keeping them under a screen with different size containers.
Prune only the leaves that are shaded under heavy canopy; those will die anyway which is normal under electric lights. Healthy green leaves should be left alone even if canopy is thick; removing them will not help. In fact removing leaves can result in smaller bud. Tuck the larger fans under if you want but otherwise let them do their thing. If you want better penetration upgrade your lighting.
There could be a number of reasons why your plants tips are yellowing. Most likely culprit is nutrient burn. Could also be a cal/mag def or an absorbtion issue. It's hard to say with no info given like what is in your mix and what if any nutrients you have been giving them. If you want a "water only" grow you need to prepare the soil to sustain them through the entire bloom cycle. Otherwise you will probably need to add a soluble nutrient to keep them happy and green up until harvest time.

Leave screen on weave plant in scrog through flower stretch, after a week of flower stop weaving through scrog, let grow. Yellow tips nute burn or nute lock check ph/ppms the solution to pollution is dilution. Nute watering and proper air circulation is all during flower