CBSubs Options doesn't handle text fields, but it's a solid starting point for a developer to make a plugin that does add text fields. My above auto actions example however does add a text field.

However, on the backend, we manage cases and communicate with customers with 70+ additional fields specific to each case.

Yeah that's a bit far beyond what CBSubs was designed for. You might want to consider using a 3rd party form extension to collect that kind of information.