Can I create more databases or database user credentials?
Seravo's WordPress service is meant only for WordPress sites. WordPress needs one database and one credential, and those are there for this purpose. We don't offer additional database credentials for the same price or plan or any other arrangements for other applications.
We recommend doing integrations between WordPress and other applications by using the WordPress REST-API interface. Making changes to the database or integrating applications directly bypassing WordPress might lead to undesired surprises in the future and considerable additional work for maintenance and development. Therefore we don't recommend it, even if it might seem like a convenient short-term solution.
See also the answer to the question Can I install software other than WordPress on the server?