Yes I feed water soluble nutrients. 5 parts nutrie...

Start a "flush" once there are about 95% brown pistils/hairs and harvest about 10-14 days later when there are 98-99% brown pistils/hairs. You still have a fair way to go with bud development..........maybe another 3-4 weeks..........it is too early to stop feeding now.

I wouldn't flush until all the trichomes are starting to turn cloudy. Can be a week to two before the trichomes finish development. And your plant is still a week or two away from that point

I may not be the best to answer this one because I'm more on a different style. i do mix in some water soluble nutrients but only an organic cal-mag and liquid kelp. i stop with the kelp around week 4 of flower and cal mag until week 6 of flower and i use molasses to help ph my water down to 6.5. I'm thinking about adding some water soluble silica to my plants. I would add some of that if you have it, but other than that it looks like your plants may have slight excess so i think you could get away with tapering it off and save the nutes depending what week you're on.