Custom content types to simulate one-to-many and many-to-many relationships

I have been charged with designing a wp plugin for surveys/auditing. A company gives my client a list of their customers. My client calls those customers to ask a list of questions to be rated on a scale of one to five, and posts the results to a web site.

I know how to do this if I am creating my own tables: table for companies, another for type of business, another for the survey itself. I’ve never really built a full blown application for WP,so I was wondering how feasible it would be to do this with custom content types. I can use a plugin to create the CCTs, I suppose, but is there a way of doing it without having to write my own plugin. I’m not afraid of writing my own, but I wanted to make sure there was not an easier way of doing it.