Install ExtendedReport by Eileen, It provides additional reports with lots of options.
Or make sure you have 'Is this Field Searchable?' option checked for the custom field that you want on the report. If not then edit the custom field and check the option 'Is this Field Searchable?'.
Shaun, Welcome to CiviCRM SE,
You will need to
Add a custom group extending participant (CiviCRM >> Administer >> Customize Data and Screens >> Custom fields)
Add custom field of type select/radio/checkbox in a custom group created in #1.
Include this custom field in your profile which you are thinking to include for event.
Note: Custom field UI doesn't ...
if you carry out a contact search (selecting the group your interested in) and select all of the results, one of the actions you see in the actions menu will be to add them to an event (Register Participants to an event). Have you tried that approach?
Once registered you'll be able to carry out all the tracking/reporting you've highlighted.
At administer - system settings - directories, there's one called custom php path that contains a folder path. Go look in that path in the filesystem and you probably have a customized version of CRM/Core/BAO/UFGroup.php. It will need to be updated with some recent changes that were made to the real CRM/Core/BAO/UFGroup.php, in particular the addition of the ...
From the backtrace, it looks like the error is due to the participantlistemaildisplay (https://github.com/voiply/com.servnettech.participantlistemaildisplay) extension enabled on your site.
To fix -
Try disabling this ext from civicrm/admin/extensions?reset=1.
Create an issue on the extension repo - https://github.com/voiply/com.servnettech....