I am not sure the maximum number of fingerprints that can be stored is. however I do know that the fingerprints and database are stored within the sensor. So I don't think you could share the sensor between different arduino.
You can store up to 162 prints on the scanner. The manual appears to have functions to access the fingerprint data on the scanner, but we do not have library support for those functions (The English version was not available when we were developing the library).