Here are a couple of tips for assigning friends (or enemies, for that matter) to characters.
Once you've got the proper number of RSVPs, you're ready to assign characters to your friends that are attending. There are a couple of rules of thumb for this.
You can host a Murder Mystery, and it's a lot of fun. We went from buying one to writing several. It's a blast for your friends to dress up, come over and play parts...