Yep, air bubbles in the drain water line, unless your brand of control valve adds them, like Clack, are not good.

They indicate that the brine line or something else is allowing air to be sucked into the resin tank (or the air is coming in with raw water) and... the only way air can get out of the resin tank is during a regeneration, specifically backwash.

Otherwise it sounds as if ya got a good plan for your installation.