1) I'd Go Bluetooth. Works Great. Cables look awful and make it more awquard to jump in a friends car with.
2) Should have no problems using your Mobile and headset via Bluetooth, Won't get any interference or anything.
3) Updates to TomTom are available and are Free. Although !!! as yet I have not applied or seen a Map update available. I'm Using TomTom3 with latest Updates and driving down the M6 Toll shows me in the middle of fields. But updates are supposed to be posted according to their FAQ section.
4) Go for CheckPOInt for your detection software. It's FREE and works excellent. It'll start TomTom for you. I have my Calander button re-programmed to start Checkpoint. Get in the Car. Turn on the PDA and hit the button. Within ten seconds, TomTom is active, Detection Software is running in the background and I'm not having to connect cables up for the GPS because i'm using bluetooth.
Paul