12c multitenant architecture - how does it scale? (PDBs?)

When laying out a server for Oracle 12c (Windows 2012 e.g.) what is a "footprint" for a PDB in terms of physical memory ?

E.g. we would like to have a server for testing customer databases with our application. We would expect serving 10-20 single PDBs on that server.

Would that be feasable to build?

Or would it be possible to swap in/out PDBs on demand, so to say, having them stand by.

How could the process of activating/deactivating PDBs be automated (script) ?

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Christoph