All good suggestions, but mine is: Start with something redundant.
Do you use Google Drive? Set up Nextcloud and use both for a while.
Also, decide on user management first. It’s way better to have a central system for managing passwords/etc. Personally I use an Active Directory based off Samba4: https://github.com/Fmstrat/samba-domain because it’s got LDAP and expandable with Keycloak to OAuth and OIDC. This may sound overwhelming, but once you learn what they are, its fairly straight forward.
Same. I can barely even tell what “good” Ubuntu brings to the table other than the task bar icons, which I just add in with am extension.