Simple default RSVP in events collection... how can it be done?

Case:
I have an event collection that is used to post new events once or twice every week. The events has limited seats, so I want the viewers to be able to sign up to the event directly in the event post and that their name (and number of sign ups) should be visible in the event post. (using Facebook Events embeds is not an option).

@PixelGeek showed this very nice RSVP using Zapier, but this has to be linked up to Zapier for every event.

Question 1:
How can I set up a RSVP system that will work out-of-the-box for every event posted?

Question 2:
Is it possible for the sign ups to opt out again with e.g. sending in a new form submission with a exact identifier like a phone number and an “opt out” checkbox?

Or:
Anybody know of a simpel RSVP plugin/widget that has these functions and can easily be embedded in an collection item?

:thinking: :thinking: