@leorock if you are fasting, taking BCAA's technically would break that fast depending how strict you want to classify it.
you can creatine or glutamine whenever the hell you want, glutamine likely helps recovery, particularly your gut or immune system (i haven't taken it in years). you can get plenty of glutamine in your diet via sources of glutamic acid I think
creatine supplementation spares arginine though Guanidinoacetic acid may be more optimal for that purpose. while creatine is made with glycine, apparently it does not inhibit glycine stores in the body (I think this may have something to do about creatine stores being recycled in the body)
you might as well take Creatine on rest days.
You don't need to take BCAA's on rest days unless you are not hitting your protein intake.
when I supplement Creatine, I usually take it on rest days unless I forget or don't feel like it. It's no big deal tbh since the body stores like 100-150grams of creatine and we only use 2-3grams/day besides exercise.