Well, offering domains isn't a bad thing. Though many hosting customers, most likly will not buy it from you. Why? Because if a user has done their research, they know "some" (not saying you would do this) companies keep the domain. Therefore, the user is stuck with them or has to leave their domain with the company.
Yes you can probably get it back someway, mabye through ICANN. But really, who wants to go through all that?
As for the knowledge base, either just create one or better yet, use a forum and have a specific forum for ALL FAQS.
All the best.