Can more than 10 devices be associated with one Apple iTunes account?
More than 10 Apple devices can not be associated to a single Apple ID.

A single Apple ID can be used to log into upto a maximum of 10 Apple devices where no more than 5 of them can be macOS devices.

A Family sharing group can consist of upto 5 members (apart from the organizer). Each of the 5 members setup their devices using their own Apple ID.

The original limit of being able to use an Apple ID on upto a maximum of 10 Apple devices apply to each family member.