Thanks for reaching out. As there are multiple right answers to this question (mainly depending on your existing architecture), I will try to answer the question as far as I can.
When deploying a multi-app (Mendix) landscape, it's a best practice to use separate credentials for each application. Preferably even per environment (TEST, ACCP, PROD). In a Private Cloud offering, it's also possible to use a secrets manager (like AWS Secrets Manager) to manage your (database) credentials more efficiently.
I'm not that familiar with Oracle (pluggable) databases, but just to be sure; you'll need a separate database for each environment/app, as the Mendix version on each environment may need a different schema when you change the domain model. If it's possible to host multiple database schemas within the same pluggable database, you might be able to use the setup you described.
Hopefully, this helps