in our Monaco, the ducts in the ceiling are continuous.
We often run only the front A/C during the night to keep it quieter in the bedroom, plenty of cool air comes through the ducts.
I'd guess if you need to save money on power, turn the temp up a bit. Costs way less to hold 80 than 75, right?
Not sure trying to isolate the bedroom is the best choice, and then what happens when you go to use it and it's 90 in there?
It requires a lot less a/c to maintain a temp than to achieve it, especially if the nights are cool and you can leave the units off at night.