Josh can give you the definitive answer but for the normal workload a MiaB instance undertakes it is fine. Nexcloud is used primarily for it contacts, though I use it as a file store too.
If you have many users, (1000s) then a simple all in one solution like MiaB is probably not right for you. If you expect a lot users to sync files then separating Nextcloud from MaiB is a relatively simple option. You can sync the address book, users etc between the various instances.
Sqlite is easier than the alternatives. That’s really it. In striking a balance between features and making the project easy to maintain, I went with the latter in this case. There’s no plan to change it because I still want the project to be easy to maintain.
No guide but the source code is available. Unless you have the skills available I wouldn’t recommend a fork. MiaB is very opinionated code but if it ticks your boxes it is a very easy low maintenance solutions for small to medium sized organisations. It is also very standards compliant and passes most tests.
You haven’t really been very open with your requirements, so it is difficult to suggest alternative projects or products.
Good points and sorry for not being open with requirements.
It’s just that Nextcloud itself under Administration shows a yellow warning that this type of database isn’t recommended. Why Nextcloud complains and that their requirements are, I don’t know and haven’t researched yet.
You can host your own Nextcloud instance on a different server away from your MIAB instance, and still use MIAB’s built in NextCloud just for contacts and calendar sync instead.