Hello;
Here is a guide on how to migrate packages in feeds: https://inedo.com/support/kb/1168/proget-feed-migration
As far as users and API keys, we don't have a supported migration path for those. However, many users have simply "copied" the data from one database table to another. The tables are Users, Groups, UserGroups, and ApiKeys.
IF the configured encryption key in both instances is the same, it will still encrypt/decrypt fine.
Best.
Alana