If you haven't already settled on one, you may want to check out [link|http://www.silkblogs.com|Silkblogs] which has all these features. Comments have rich text editing and you can add attachments to comments too. RSS is avaiable not only on entries, but also on Comments and Trackbacks.
It seems to have been built specifically with business usage in mind. In addition to the blog, I understand they are working on integrating chat, survey/polls, and vlogging to create a full collaboration/communication dashboard.