Sounds like an interesting project!
Have you seen our single sign on document? Setup DiscourseConnect - Official Single-Sign-On for Discourse (sso)
If you want clients to only be able to access their own data, then yes. You can run multiple Discourse instances with minimal overhead using a multisite configuration.
If you are interested in a hosted solution, feel free to drop us an email at team@discourse.org, and we can discuss. If you’re looking at self-hosting, there are a number of independent consultants here who might be able to help you out. marketplace is the best place to post when looking for consultants.