Tammy,
Because general-comments are not an object type, you can't create a search service contract for just general comments. You would have to associate the service contract with acs_message.
A refined general comments data model would directly subtype content_revision and store comments in the content repository. I am not sure how to handle attachments. I like the idea of handling upload of attachments in a standard way, but I don't feel the attachments package is the right way to do it.
I will post a new plan for a general comments data model and api in the next week for review.