In addition to my note above - if there is no way to edit the Forum - Registration page, are there other registration plugins that are compatible with wpforo? If so, which ones?

I understand Ultimate Member and Buddypress are compatible, but they both have WAY more features than I need - I really am only looking for a simple registration form that tells users they have to be approved before they become a Forum member. 

I look forward to a solution. Thank you!

Dashboard/Forum/Phrases search for the phrase "registration" , edit the "after registration..." entry to suit your requirements. 

Is there a way to customize the Forum - Registration page?

Currently the form says "Join Us Today!" - I would like to be able to add a note there that tells the user their registration will need to be approved before they can complete the registration (by setting a password).

All phrases can be changed/translated in Dashboard > Forums > Phrases admin page.

wpForo Phrase Documentation: https://wpforo.com/docs/root/translation/quick-translation-phrases/

In addition to my note above - if there is no way to edit the Forum - Registration page, are there other registration plugins that are compatible with wpforo? If so, which ones?

You can install any plugin which have registration form, then navigate to Dashboard > Forums > Settings > Members admin page and change the Authorization URLs to that plugin page URLs.