Not sure about using an NAS in conjunction with a Time Capsule, but you could hang a large external HD off the Time Capsule's USB port and store your movies on that.
+1 for Handbrake as a DVD ripper - the best there is on OSX, no question, and very, very rare to find a DVD it can't handle; I use one of Handbrake's built-in presets for all my DVD rips, and files are all iTunes/iOS/MacOS compatible MP4/M4V. If you have any AVIs then you can either convert these to MP4 using Handbrake, or just use Airvideo like Caltsar suggests above to stream to an iOS device.
I don't own an Apple TV (still waiting hopefully for BBC iPlayer integration here in the UK) but my understanding is that it'll stream anything you have in an iTunes library (photos, movies, music, podcasts) to the TV it's connected to. From what I've seen the Apple TV front end is very similar to Front Row i.e. pretty painless to use. If you're already Mac/iTunes based I wouldn't look at any other media player, personally, as I think it'll do everything you want.