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) [email protected]

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: [email protected]

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: [email protected] (as you explained)

2) keep whatever you're using now.

Just forward 1) to 2). Then you can start handing out the new email.