For the dedicated database addons, you simply point and click on the dashboard to install them. They are exactly the same prices as the app containers. For example if you wanted a 1 GB RAM MongoDB database with 10 GB File storage, that is $10.36. After the instance is provisioned, you can simply use mongo shell to log in and initiate a replica set. This will start the local database which provides the oplog functionality.
To scale out on OpsCaptain, you will have to say create multiple apps, app1.opscaptain, app2.opscaptain, app3.opscaptain and then use Cloudflare to load balance to them or you could use the Cloudfoundry Nginx buildpack.
We basically provide the basics and you decide how you want to use the platform.