

I assume you basically want protection against disasters, but not high uptime.
(E.g. you likely can live with a week of unavailability if after a week you can recover the data.)
The key is about proper backups. For example, my Nextcloud server is running in a datacenter. Every night I replicate the data to a computer running at home. Every week I run a backup to a USB drive that I keep in a third location. Every month I run a backup to a USB drive on the computer I mentioned at home.
So I could lose two locations and still have my data.
There is much written about backup strategies, for example https://en.wikipedia.org/wiki/3-2-1_backup_rule … Just start with your configuration, think what can go wrong and what would happen, and add redundancy until you are OK with the risks.
I don’t use Nextcloud calendars or address books. But I assume they are included in regular backups.
I pay about 50€ for all absolute overkill Hetzner dedicated server (128gb of RAM).
I live in two different flats in different cities because of personal circumstances.