Well, I usually water and/or feed FULLY each time....enough to get some runoff from the bottom of the pot. That ensures that most (if not all) of the soil gets wet during the process (that is, ALL parts of the root mass are watered/fed). So I would recommend upping the amounts you use, especially during flowering. You want all that root mass to get wet during each watering/feeding for optimal bud production.
As far as spraying goes, opinions differ....but I think most would say don't spray the buds because you may increase the likelihood of bud mold forming if the buds stay too moist while they're forming (esp with some strains that grow dense, tight buds). I do occasionally spritz with water during the early stages of flowering, but I pretty much hold off after a few weeks of 12/12...it
might be okay if you have good air circulation all the time, but why take the chance? As long as you're watering deeply each time, there'll be no need for misting, so less chance of losing perfectly good buds to mold.
btw, I mentioned the LST only because I was concerned about how much height you have available in your cab. I just had to remove one plant from my cab, since it stretched up into the lights and started to burn. I didn't have enough lateral room to LST, so I would have had to top after 2 weeks of 12/12 (cutting off small buds), and just wasn't worth it. I really should have put them in the 12/12 cab earlier, but there were already mature flowering plants in there just waiting to finish up. Bad timing on my part...oh well, these things happen when you're experimenting with new strains. As long as you have another foot or more before they get too close to the lights, it sounds like you should be okay. If they do get outta hand for some reason, though, LST is the way to go when you're already in 12/12. I usually use much smaller pots (0.5 to 1 gal), so they're limited as far as how tall they get since there's limited space for the root mass...last time I used 3-gal pots i ended up with 4-5 ft tall ladies (but I probly vegged longer than you did).
I would say increasing the volume of water/nutes you give them will be most beneficial as your grow continues. As your plants grow (and start packing on bud mass), they'll def drink/eat more than they do now. While some folks recommend waiting until the plants get a little dried out (slightly droopy) between waterings, personally I don't like to stress my ladies at all during flowering, so I try not to let them get TOO dry. I'm just guessing for your case, but maybe once a week for your 3-gal? And you'll probably need close to a gallon for each pot, maybe more - again, enough to see runoff from the bottom. Once you do it the first time, you'll have a better idea exactly how much nute solution you need to prepare for each watering cycle, but def if you see any signs of drying out (it'll be pretty obvious if you're checking on them daily) get some water to 'em pronto, since stress during 12/12 can decrease yields and/or or promote formation of hermies.
Also, I usually try to avoid feeding a dry plant -- I usually give them some water immediately before feeding (water, then wait 30 min or so, then feed with nute solution until runoff). And I try to alternate between water and nutes (although occasionally I will do two feedings in a row during the bulk-up phase of flowering).
LOL, another long-winded reply
Anyways, hope this helps.