NORML Joe, nice to see another bubbleponic grow. I am about done with mine maybe 2-4 weeks left.
Some things I did in the beginning to help in the long run was to cover the tote with some foil tape. Some peeps paint thiers but the tape is easy and you can do it with the water still in the res. This will help prevent some algea/bacteria growth by keeping the res dark as can be.
I added another air stone for 2 total, I was reading to have 1 watt of air for each gallon of water.
The drain helps a lot and make res changes easy.
You can also use the pump to help with res changes. Just D/C the the dripper and use a length of hose to hook to the pump and pump the res water into a bucket or something.
Once the roots hit the water ditch the drippers all together. You can keep the pump in there to move the water, but it can heat the water a bit if you are having res temp issues.
Your plants are looking real good, I wouldn't worry about cutting off the nute burned leaves, they will fall later or just look a little spotty, as long as the new growth is good, no worries.
Once you get a good res change schedule and figure out your feeding schedule, its easy as can be. I would recommend getting a ppm/ph meter you'lll want to keep an eye on those daily, or every other day. Also, you can check your tap water to make sure its good.
Good luck man, your off to a great start, check out my grow if you get a chance, just click my sig.
Peace!