Reduce master volume to create headroom for mastering?

Hopefully I won’t drive the ME nuts

Wishful thinking.

and he will tolerate a newbie

Tolerate, maybe. Probably if he is relatively new, and/or is not a brand name. If he is a brand name, he’s more than likely going to be annoyed at you if you didn’t provide him with something useable. Does he know you are a newbie?

(and provide feedback?)

Not if you dont ask - no he won’t.

Thing to do is:

  1. touch base with the ME before sending anything over. He/she will tell you what they prefer, in terms of level/headroom, compression, etc.
  2. Take what the bandmember says with a grain of salt. Most musicians who are not engineers think they are, and think they know their stuff.

Cheers.