Other than Battle the Witch.
Yes. The exact logic is: Progress is always saved, except when a new multiball is started (not just resurrected via Glinda), any consumed savers will then be reset to be able to be used again.
Yes, totally independent progress on each.
No, as above. Guess I jumped the gun a bit.
Progress during single ball play is remembered separately from progress during multiball play. Progress WILL be saved for multiball savers if you start a new multiball later, other than to reset consumed ones. So, e.g. you can play ECMB, drain out the left outlane and get "THERE'S NO PLACE" on your way out, drain out of mb, then later start a completely independent MB and you will still only need "LIKE HOME" to get a ball back.
No, similar to Glinda, the ability to use them only gets reset at the start of a NEW multiball, not a resurrected one. If you didn't know, for example, you can start ECMB, get Glinda for AAB, start Rescue, get Glinda for AAB, start Crystal Ball, get Glinda for AAB, etc. If you start a new mb, your ability to cash one of these things in is lost if you didn't use it before starting the new one. I.e. start ECMB, then start Rescue, then hit Glinda for AAB. Glinda will not give you a 2nd mb until another 3rd new mb is started.
The one thing you have to remember, though, is Glinda will NOT ever give the same thing back-to-back (except in the rarest circumstance she has nothing else to give you other than points, but that is almost impossible to pull off since Glinda is generally available when HOADC is available, so there should always be at least 2 things to swap between (horses and points)).
Most of my mystery awards follow the same rules.