Hi Michelle,
There are a couple of threads on this. They mostly relate to throttling certain kinds of emails internally using Smart Lists or Static Lists to manage the number of emails. For instance, at one firm I had to limit "Promo" emails to no more than twice/mo which meant having a couple of smart lists looking for people with Was Sent Emails CONTAINS "promo" IN PAST 30 days.
And then having that group as part of a standard suppression list.
For your need, you might try the following:
-tell people on the subs page how often to expect emails for each option.
-to throttle each option, try running a list automater to put a lead into a static list each time they want a certain kind of email. So if they say "Send me a Blog Update once a month" they get put on that list. of course then you have to have some logic to say if person is on Once a Week, it is ok to send this Email or Once a Month, it is not ok yet. There might be a manual item where you run separate emails for each type of Channel+Frequency.