There's no reason not to go to Paris on a weekend. May is a beautiful time of year to go.

We drove our own car from Germany to the UK and back in 2 weeks last summer, and that was a LOT of ground to cover, so I think your plan sounds awfully ambitious. Do consider flying and/or train travel for at least some of your trip, or else eliminate a few destinations. We are all about car travel ourselves, so I understand your DH's perspective, but sometimes it just doesn't make sense.

And to add to the clarification about taking your car through the Chunnel: Imagine driving your car into your garage and close the door. Have someone shake your car from side to side for about 30 minutes. Open the garage door and drive out. That is pretty much the Chunnel experience. If we had it to do again we would take the ferry - at least there's a view!