I would not be terribly concerned about bubble count, but rather use your target pH as a goal. You have to start somewhere, though, so I'd try 2-3 bubbles/second or so and see what happens over the course of the day.
Do not get your calibration packet near your tank.
I don't know the exact pressure pressure, but you don't want it to run completely out. Hopefully when you turn your tank in they will just exchange it for a full one on the spot so you don't have a delay in getting it hooked back up.
I think you DO need a check valve on your CO2
tubing if you are using a controller. When the controller shuts off the gas, the tubing will tend to syphon water down. I don't think it can go anywhere (someone correct me if I am wrong) but it just takes the gas more time to force the water out of the tube when it does turn back on.