looking to have mac mini based setup.........

but i have some questions

what we want to do is get a new mac mini (late 2009) and run plex. i have read that plex can grab media from the itunes library and want to use that feature when we add an apple tv or 2 for the kids rooms.....basically set it up so we can stream movies upstairs.

i will add some external usb drives to the mini for now for storage ( and suggestions for reliable quiet externals are very welcome)

but i have a few questions that i am not sure how i would work around..

1. i like to rent and buy dvd's and blue-ray and rip them to mkv...i know plex can do mkv but itunes cannot....since i want movies to be apple tv capatible...how should i handle this?

2. the gf and i....well our musical tastes overlap but are generally different...should we just keep our tunes on our own machines and not the mini?

3. how many apple tv's can simultaneously pull from a single itunes library at once?

4. How would apple's "home sharing" feature in itunes help me with the setup i want to make?

thanks all!