My boss wants a gradual roll out of the apps not a big bang.What you mean by upgrade here? Start using APEX 4.x new features like Anychart 5 and dynamic actions or something else
So I will upgrade one app, test and then issue to prod.
Then I upgrade second app, test and issue to prod etc.
We currently have a dev, test and prod environments.If I understand correctly you have only one DB. In that db you different workspaces for dev, test and prod.
1 database with many schemas.
12 workspaces, each with 1 application and 1 schema.