19c : CDB / PDB Architecture

Hello,

We would like to switch to Multitenant architecture of 40 applications under Oracle 19c.

Each application has 2 Development  environments and 2 Testing environments on the same database server.

Example: HR Application  : HRD1, HRD1, HRT1, HRT2

What are the criteria for grouping PDB databases by CDB.

Should the DEV and TEST databases of the same application be combined in the same CDB?

Should we group all the dev environments in the same CDB (CDBDEV) and all the test environments in another CDB  (CDBTEST) ?

Should we group the applications taking into account the typology of the application (Transactional, DSS, ...).