Hey Jan,
Although I personally am not a very big fan of iTunes (as it is as restrictive as all other Apple products – I DO own a MacBook Pro, an iPad and an iPhone LOL, it works fine if you want to do it the way Apple intended), it is good to hear you are finding your way with it.
For question #3, you can “lock” tracks in Traktor to prevent stuff from being written over. Unfortunately I am not exactly sure what tags that entails. I know for a fact it includes BPM and beatgrid. Anything else you might need to check out.
Greetinx,
C.