The major data constructs in WP Issues CRM are as follows:
-Constituents (possibly classified by custom fields)
-Issues (posts tagged or categorized)
-Activities (which belong to a constituent and pertain to an issue). (Comments are really a special kind of activity, although they have their own data table in WordPress. We associate comments with constituents through the email address recorded with the comment record.)
If you want to associate constituents with an issue, they need to have an activity with respect to the issue — e.g., send an email about the issue. You can create custom activity types, through the Options submenu if you want to link issues and constituents without an activity like email. You could define an activity “Has an interest in.”
If you view an issue, you’ll see all constituents with activities associated with the issue. And conversely viewing a constituent shows all activities by the constituent.
If you just want to classify constituents, then you can add custom fields and options for those fields through the Fields and Options submenus.
I think you’ll be able to do what you want to do. I wouldn’t use tags — that will be very hard to keep organized.