If you put them in the buckets soon, you will have to pour nute mix down the pebbles close to the plant because the rings are too far away from the roots to do much good. I think the real purpose in drip ring is to put oxygen in the water, not necessarily wash the roots with nute mix. You'll have to keep hand feeding until roots are established down into the bucket where they get nute mix.
Is that a fan at the bottom? If so you might want to hang it up top because heat rises and in such a small space you want to suck out most of the heat as quickly as it's made. This means placing a fan at the top of the grow space.
Your grow bucket are a dwc type system except where dwc shoots air into water, drip ring puts oxygen into water by having it pass or hydroton pebbles. You can take you ppm's higher in dwc methods because there is actually less oxygen than aeroponics, which uses a lower ppm. You could probably take your ppm up to 750 or so. The ppm goes up as you see it doing because pH down is actually a fert. It's causing your ppm to go up and pH to go down. If you use actual fertilizer to raise your ppm, you should see your pH drop some, giving you a more balanced ppm/pH ratio.
If you don't pour nute mix over the hydroton several times a day, you're going to have to find a way to get the roots down in the water like remove alot of the pebbles and raise the water level. I suspect you might be giving too much light in such a small space, you'll have to cut them back frequently to keep them contained in that small space. If this works right, they'll start to grow like crazy.