I just migrated all of my aliases to addy.io, but I was also fortunate in that all of my aliases were based on a domain that I own. It was a simple as exporting the alias list to a CSV, formatting it a little for addy.io, then importing it!
If all of your aliases are based off of simple login domains, then that’s gonna be a lot harder. You’ll have to change your email on all of your. If that’s the case, in the future, I would definitely recommend getting a second domain for generating these aliases so that migrating is the problem in the future!
As for addy.io, I honestly love the service. The Lite plan is plenty for my needs and only costs $12 a year. That and Bitwarden are a steal imo.
I have a Nextcloud Instance that’s been pretty solid for me for a couple years, but I don’t use their all-in-one image so I can’t comment on that. I do use Radicale instead of Nextcloud’s calendar/contacts though and I removed basically all of the Nextcloud apps except the file sharing. Idk why. I just don’t like when everything is in one thing lol