Problem: Too many junk/novelty accounts being created

[weex]

Though by this time hundreds of accounts have been created and profile info added, the vast majority seem not to be in use.

Proposed solution:
Require email confirmation or account approval based on some question to be answered in signup.

[Mansh05]

How about request to join feature like in some of the instances of mastodon. Here they will share the intend of joining the instance. There for the admin can moderate and choose to accept or reject. This aligns to the proposed solution that you have as well.