Good evening Angus and welcome back!
Thank you for reaching out to us.
We will gladly try to answer your questions.
1. How can I trigger an email upon the approval of a community event that is pending?
If I understand correctly, what you would like is that the administrator gets an email every time an event is submitted, right ?
If that is the case, I would recommend trying out one of the following plugins for that purpose:
2. How can I insert some words to the effect that their event wont get published immediately and is being held for moderation?
The easiest solution to this would probably be to edit the Add Event template to display a message at the top of the page.
To do that, you need to read our Themer’s guide. Look specifically for the section titled Community Events.
To make a long story short your own template will now have priority over the default plugin template.
Let me know if that helps.
Have a great weekend!
Geoff B.