If anyone is going through 20 lbs/week, they’re doing something wrong. Either they have too small of a tank for their grow, they have the PPM’s up WAAAY too high, and/or running it during lights off and/or are evacuating it through their ventilation throughout the time they run it. I’ve had (2) 20 pound tanks that I used to rotate and went through one of those every month or so.
So my room is pretty much sealed. I vent my HPS lights through a sealed ventilation system, so it doesn’t pull anything from the grow room. It pulls cool air from outside the room and runs it over the lights, then sends it out through the dryer vent (unless it’s winter time, then I keep the heat in the basement). Here’s one of the lights, which is connected to another one that has the same hood.
As for the accessories, I’m using a Vivosun regulator. I don’t know what solenoid they use, sorry. And I’m using an AutoPilot APC8200 controller/monitor.
It’s really hard to say if you need to do any caulking. If you blow smoke in your room and can watch it escape, it might be worth sealing it up. As you probably know CO2 is heavier than air, so it falls down. You’ll be using fans as normal, which will help give you equitable distribution within your room, but it’s unlikely that you’ll be blowing any of the CO2 out through the ceiling lights.
Hope this helps. I’m not sure I answered all your questions - you had a bunch of them! 