The N deficient leaves won't recover. Watch for new leaves turning yellow as a sign of whether you've corrected or not. Long-term, you might want to start collecting rain water.
I had to go out of town for 5 days and I bought a "patio" watering kit with a timer at Home Depot that worked great. I set it up two days before I left to make sure it was working right. Like others have said, though, being gone for the weekend shouldn't be an issue if you water them heavy...
Very hard to see anything with the HPS on. How many weeks did you expect to go? It wouldn't hurt to give them some N if that's really what they need but not sure there's much point this late in flower.
After all the problems I had in my first room, I build in extra capacity for air-flow, temperature control, and humidity control. The only thing I never have is extra height, so I have to very disciplined in veg.
You don't have to, but I do because it makes the plant stay lower. What I do is wrap a 3-4 inch piece of garden wire around the stem at a 45 deg angle to keep the lower part of the stem above the bend point at a 90 deg angle. I didn't have to actually roll this stem because it's pretty thin...
You can get a 16 slot coco starter tray at Home Depot. Get some Rapid Rooters and Clonex. Always have a node near the bottom of your clone. Lightly scrape the bottom of the clone with an exacto knife. Dip in the bottom of the stem in the Clonex. Insert into RR (I like to use them upside...
If you look up supercropping, I'm sure you can find a video. You grasp the the stem at the point you want to bend it between your thumb, forefinger, and middle finger and gently roll it back and forth. You'll feel the fibers snap a bit but you don't want to snap the stem. The second time I...
I wouldn't strip anything at this point. Just top or FIM above the last node. Never strip anything getting light, IMO. If you want a clone, wait until you have two more nodes.