RE: hire car??
I've just taken a hire car over to France, I'd say the chances are you aren't covered, you will need.
European insurance cover
A European driving kit (includes hi vis vests etc)
Some car hire companies also insist that even if you have the insurance you travel over on the chunnel and do not allow ferry crossings (probably because of the amount of bootleggers getting vehicles impounded).
All in all, I wouldn't bother.