Hey Robert,
With only Mendix and PostgresDB you won't be able to do it (sooner or later Postgres will get in trouble), you need file storage e.g. S3.
FYI, in my current application I have more 15,000 files each file is around 10 MB and everything work as expected.
https://docs.mendix.com/refguide/custom-settings/#commendixcoreStorageService
Best regards, Slavko