Drupal 8 user roles and content access

I have the following requirement, but can't seem to find a workable way to implement it.

I'm building a conference management system for a client. It currently uses the following workflow:

1. A user with the Conference Manager role creates a new conference using the Conference content type and creates an ID for the conference (cid) as a taxonomy term
2. Each subsequent node related to the conference is associated using the already generated term (terms can only be created in the Conference content type)
3. Conference Speaker Profiles & Conference Partners Profile (content types, not roles) get associated in the same way
4. Taxonomy terms are then used to sort content (from different content types) into views - e.g. all content tagged with conference_1 displays on a page, conference_2 on a page, etc.

I would now like to associate the taxonomy term as a field within a role e.g. a user with the role of 'Conference Delegate' and associated taxonomy term of 'conference_1' can see all content in the conference_1 view (and possibly edit their profile where permissions allow and contact other Conference Delegates/Conference Manager/Conference Speakers attending the same conference).

Currently I'm using the Multiple Registration module to register my users and assign them a role (Conference Manager, Conference Delegate, Conference Speaker, Conference Partner). I've set up the register links for different conferences to pass a variable into the url (www.example.com/register_delegate?cid=conference_1). I now need to find a way to get that variable back into the user registration form and store it as the taxonomy term value (I got this working somewhat using a hidden field in the Webform module, but can't seem to get it to work in the registration form as there is no hidden field entity - that I can find - to get the variable from the url and then store it as a taxonomy term). I then need to find a way to associate the user role with the content based on the shared taxonomy term.

I've tried the Permissions by Term module, however it seems its permissions are not granular enough for what I require (content with x term is coupled to a user role instead of a role with x term coupled to content with x term). I have also looked at the Group module but I can't seem to get the registration process to sync in a way that user data is accessible in a single view to an admin, who can then perform actions like emailing all users with the same taxonomy term or role or both.

I would greatly appreciate any input that could point me in the right direction, or suggestions on achieving this some other way.

Many thanks in advance.