Hi Eric,
There are entity limits on Self Service and Free subscriptions as detailed here, which include Applications (Clients): Entity Limit Policy
We also support dynamic client registration, which may help your use case - https://auth0.com/docs/applications/dynamic-client-registration
I’m not certain I understand your use case from what you’ve mentioned, but these docs may help you with the design to fit better into Auth0:
Kind regards,
Steve