I finally got one email on Tuesday saying there'd be another email that night or the next day with instructions. Still haven't seen anything.

Same

Interesting. I scrolled through the guide and one thing that was unclear is where does the adb.exe file come from?

I've been using Proton Mail and GrapheneOS for some time now. Early in I found an app called You Have Mail that solved the pushnotifications problem for me. I've never used Tutanota, so I can't speak for it at all, but I really like Proton.