There is tons of info available in both the Mini and Apple TV/Home Theatre forums about this but I'll hit a few points that pop immediately to mind:
- While a new Mini will work great as a HTPC, it isn't necessary, even for viewing high bitrate 1080p media. I'm currently using an early 2009 model (MB463LL/A, 2.0 GHz C2D) and it works beautifully--serves my media to all my iDevices and 3
TVs as well as the living room TV to which it's connected. I have no experience but have read that the older Intel C2D and I believe even the Core Duos will get the job done as well. If you want to watch blu ray rips (.mkv) without encoding, you will want to stick to more recent models but if you plan on encoding with something like Handbrake to .mp4 (smaller file size, lower bitrates, you can save a few $ and pick up either a refurb from Apple or check out eBay for an earlier model.
- PLEX is great, for everything except an video purchased from iTunes (damn DRM
). Unfortunately Apple removed Front Row (native media interface in OS X) from Lion but if you run Snow Leopard on an older Mini, you can use that for iTunes purchased content and can even launch it from PLEX.
And yes, an Apple Remote works just fine but is not necessary. You can program a universal remote (Harmony remotes work great) or use any number of apps (tons for iPhone/iPod Touch, probably a bunch for Android but again, no personal experience), include PLEX's own apps. As mentioned, I use my Harmony One but have also used Hippo Remote and Rowmote (personal choice) on my iPhone. For the times I'm actually navigating around OS X outside of PLEX, I use Air Mouse in lieu of a mouse/trackpad or keyboard.