A couple iTunes questions

Currently, all of my music is stored on my desktop PC on a secondary HDD (G). I'm am syncing 2 iPhones and one iPod Touch and I have some questions.

When I purchased the iPhones, one for me and one for the wife, I set her up with a second user account on the PC. I had read that if we were both to try to sync to the same library I would be running into problems. I wanted both of us to have separate playlists, address books, notes, etc. My problem now is that we can't share music and applications without a bunch of extra work. For example, when I purchase a song on my iPhone, I have to manually add it to her library. I was also under the impression that we could share applications, so we didn't have to purchase two copies. Is that correct?

Also, when adding all the TV shows and movies I have saved, I have to do them manually and then set the info for each show so it matches mine and shows up in the right place.

Is there a way to fix this?

Also, I would like to move all my media to a NAS running RAID 1 just so I don't have to worry about a HDD crash. Is there a way to move all the media and library to the NAS and still be able to sync the iPhones and iPod Touch. I have read conflicting arguments about syncing to an external library. Would it be best to keep the library on the local PC and just move the media?

Also, if I were to move the media, I know my links in my library would be broken, but what if I mapped the NAS drive the same as my secondary drive. For example, the current HDD is labeled G, so if I mapped the NAS through Windows Explorer as G and kept the rest of the file path the same, would have work?

Thanks for all your help and sorry for the long post.

Well, I guess I have some work to do. I've posted this same question on three different Mac forums and haven't gotten an answer on any of them. I'll post back if I end up figuring everything out.