I also recommend Plex for the Mac mini. I use a similar setup, but without an Apple TV. I have the mini connected to the HDTV via HDMI. The Plex iPhone app serves as a great remote and the Plex database includes media files spread over several computers and hard drives. It's a great way to organize, manage and deliver movies, TV shows and music videos, streaming them to any computer or iPhone on the network.
While doing all of this, the mini also serves as a desktop computer with another display, running Skype, Mail, Safari, TeamViewer, MS Office apps and much more... all simultaneously with ease. I also manage the mini remotely through Screen Sharing from my MBP.