Yes- the number of buckets is an application level concern that depends on the use case. So it’s definitely not the case of
Security, multi-tenancy are typically the reasons to have multiple buckets . That said, one should be wary of the number of buckets - there are performance implications to having too many of them.
You may be interested in this post that advocates against creating too many buckets. This is from our own server team. It also provides some relevant links that would be good reads.
So specifically in the use case discussed in the original question there is no reason to have more than one bucket.
The choice of database comes down to the application needs. NoSql is best suited for certain kinds of applications and Sql for others. There is also a paradigm shift in the approach to data modeling and data management - all of which is discussed in our Couchbase server docs…