Advice needed

Jjnsgy wrote:
Other than apple and roku, there are no other options.

For Plex there is a Samsung client (if you have a suitable BlueRay player or TV), plus the team just released a Google TV client. There are many non-Plex options as suggested in the previous post, and other media servers also. I just recommend Plex as I find it to be the best out there at the moment, though it is currently better for video than audio.

Am I correct in understanding that the plexapp media server only presents the media data and therefore I would not need to duplicate the data for a non-plex extender?

Correct - Plex never touches your media, so it is fully accessible to other applications, extenders etc.

you also mentioned that plex can organize various copies ripped at different resolutions (eg 1 bluray and1 for iPad). Do I need to set up 2 separate folders?

That choice is yours depending on your need/setup. If you place two copies of a movie in a folder, each with a different resolution, then Plex will index both but present them as a single library entry. Then when you wish to play the movie you will be asked which version and be presented with basic metadata to allow you to choose (eg between a 720p encode and an iPad encode)

Similar question for music. If it is stored as an iTunes db, I assume I need a second copy to be accessible by non-iTunes clients (eg droid).

Not necessarily - most applications like Plex & iTunes can access the same media. The key is if any of those applications change your media in any way. For example iTunes can organise your media into a Artist/Album folder structure. If it does that you may have to force your other applications to rescan the media to detect any changes iTunes has made. So a common media library is possible, just be aware of how each of the applications that access it might make changes