I did not read via all the replies, but with air brakes you have some simple rules.
1 air brakes used in short time take the air from tanks with limited capacities.
Meaning fanning them will run the supply low and has to get you into troubles.
2 I don't remember precisely, but DOT apply pretty liberal rules to air brakes.
From top of my head, with engine off when you step on the brakes and don't loose more than 3 psi per minute >> you are good.
3. If in any doubts, take it to specialist. Brakes is not the items to learn by errors.
GOOD LUCK