This is almost identical to my approach. One minor difference is that I got on the free Google Apps for Business plan a decade or so ago. So deliverability is there, which does come up from time to time. i.e. Occasionally you need support, and the service wants you to email them/reply to their email from the email you use with their service. So in Gmail, I have to set up an account/alias so I can send the email.

I did self-host this way back, using MailEnable on Windows Server. It... worked. But I don't recommend it!

The other downside is that the catch-all sometimes gets a lot of [gibberish]@[customdomain]. It's not too bad now, but there was a period where gibberish hexidecimal aliases were spammed regularly.