hmm... the email stuff we can't answer much for, as we can't see ourselves using it... However, it might also be a bit much with an email for each time there's activity in a thread with email notifications enabled. At least if it is a group RP. on a 1x1 it might be different.

one level we could see some desiring to use for email notification is this:
- on @mention
- on new IC posts

Having all the options always visible might also be a bit cluttery... especially for mobile users... maybe have a separate page or somesuch for "alter subscription notification levels"?