Yes, it should back up all of your media no matter where you got it from.
You need to contact the itunes store to sort out your issue
Yes.
Yes
The iTunes store
You can download songs by going to the iTunes Store.
No you can't store game memory on itunes, only songs.
Yes, because .mp3's work with Apple products. But you cannot use the zen with itunes, or with songs bought in the itunes store.
The iTunes store
Yes you do.
The 69 cents songs on iTunes can be found in the iTunes store. There is no set way to find these songs other than to do a search for them.
Most songs from the iTunes store in New Zealand cost NZ$1.79
You can download songs by going to the iTunes Store.