I switched to Fastmail a few months ago and love it.

My tip is: Start simple.

1. If you have any other Domains forwarded to Gmail forward them to Fastmail instead.
2. Forward Gmail to Fastmail (i.e. add as an account including importing old mails). This won’t get you off Google yet, but at least a backup and you can practically stop using Gmail.
3. For any new registration, use Fastmail (or any of its random emails etc.)
4. Slowly transition your old accounts.

Wow, that story is pretty insane.