Nice. I'd highlight that conceptually, there are two entirely separate concerns here:
1) the front, if you so will - the emails which you give out and to which people (or algos) send you stuff
2) the back, where you receive and read your emails.
For many people, for example:
1) abc@gmail.com
2) gmail.com web mailer, or gmail app on mobile, or native OS app on the computer
You suggest a complete revamp:
1) catchall at own domain: anything@mydomain.com
2) one (or several) protonmail/fastmail accounts
But it's worth highlighting that people can get many benefits already by
1) catchall at own domain: anything@mydomain.com (as you explained)
2) keep whatever you're using now.
Just forward 1) to 2). Then you can start handing out the new email.