How many cardholders can an SP-C controller have in them that are available while offline to the Server?
Available documentation does not discuss the maximum number of user objects that an SP-C can accomodate in it's local database.
The max number of Users is 5 million. This is the limit regardless of whatever else is configured in the SP-C.
The suggested limit to reference, for a typically configured Controller, is 10,000 users.