Get your timers dialed in and just don't waste so much next time. I never add my water back in mostly for fear of getting crap in my res that could interfere with the pump. Unless you're getting robbed by a nutrient company you shouldn't be too concerned about 5 gallons.
Edit: you could always...
If you're already going to get another res, pump and timer why not just have 2 separate systems entirely and mix each for the specific phases of flowering? Otherwise you'd need check valves or something to prevent pumping nutes through the pump that's not running, sounds like more of a headache...
Get those fan leaves off the plants and out of the room and into a trash bag, they have lots of moisture in them. Get em upside down too out of the trellis and just do whatever you can to keep the room around 50% humidity and under 75 degrees f or so and you'll be fine. If you still have the...
I have a hole cut in my wall and I exhaust my room constantly, mold doesn't take long at all to take hold and once it does it spreads like wildfire. Do not leave that shit in a sealed room without at least a dehumidifier. if you don't have any exhaust setup for the room run as many fans as you...
If you let bud dry out too much it will lose some taste and smell, may be a little more harsh as well but if it stays wet it will be moldy and become garbage. You'll be fine trimming half wet and half dry as long as you dry it all, then burp it in airtight containers daily until it's dry enough...
You can let it dry out as much as you'd like but it really depends on your climate. I live in a very dry climate and my plants are dry in 5-8 days typically, your mileage will likely vary but a lot of people dry for 2-3 weeks in more humid areas. Trimming while they dry is no problem, especially...
You can dry them out then trim. I prefer to trim dry so I just remove fan leaves, dry the plants out and then seal untrimmed buds in airtight buckets and check on them daily and burp until I've got it all done. I actually seem to prefer this method not only for flexibility of finding time to...
Are they feminized or regular? If they're regular I would honestly pop em all because you still may not get enough females by the time you get to late veg/early flower. If they're feminized I'm the wrong guy to listen to.
4.5 feet? Wow, I'd grow sog style with as many small clones as you can but that's just me. 3 gallon fabric pots give me some pretty damn big plants! Geopot makes fabric bed liners that come with a frame, you could buy one to fit your space and fill it as much or as little as you please to help...