divi theme multisite registration

I want to add custom fields to the multisite registration, not to be confused with profile fields, this fields should be attached to the "sites" and not the user. I'm using buddypress and I can create additional profile fields no problem, but I'd like to ask more questions when a user is signing up for a site. The site categories plugin does a nice job of adding an additional question, so I'm wondering what's the best way to add more custom fields.

All the existing questions related to this subject aren't honing in on "multisite fields" and seem to be answered by suggesting profile fields, but my questions are site specific.