Rel 12.2 Upgrade Questions

We have begun our Discovery phase for this 12.2 upgrade and are concerned about our customizations.  We do NOT have custom forms.  Our customizations are primarily procedures and functions we've added to the database and kicked usually with executibles and concurrent processes or from workflows.  And we have sql code used in Oracle Alerts.  We're thinking we'll need to update the code for these customizations to ensure the APPS schema is used rather than the individule module schemas, i.e. AP, PO...  but is this enough?  What else do we need to do to ensure it works after the upgrade?  Are