Hi Ryan!
The magic starts within TribeCommunityEvents::doEventForm() and if you follow the train of logic you will see that the submitted post data is scrubbed clean as a security measure:
$scrubber = new TribeCommunityEvents_SubmissionScrubber($submission);
$_POST = $scrubber->scrub();
To avoid fields from your own module being scrubbed out you may then wish to work with the tribe_events_community_allowed_event_fields filter.
The usual actions such as save_post will ultimately also fire when the event is created and you could effectively piggy back on this process. The rest is up to you – good luck 🙂