Looks like you are all set. The sandy stretches will overpower a road bike, but a touring bike should be OK, even if as often the widest tyres that will fit your frame will be best. We are Dutch and we live in Holland, and getting to Normandy and Brittany by train is complex. We first drove to the D Day beaches to show my son where his grandfather landed with his ship in 1944. We then drove on, and left the car beyond the bay West of St Malo because crossing the dam there by bike is tricky.