Itenerary\Logistics Questions

Maybe a combination of trains between larger distances with multiple car rentals?

You may have your solution here. Rent a car when other transport cannot get you to where you want and use rail/bus to cross borders. A one way rental ending in a different part of the same country usually has a small fee ( or none, as my experience in Italy)

There is no need for a car in Amsterdam or Bruges. There is excellent public transportation options in and around both of these places. You could pick up a rental car on leaving Bruges to explore the area around Bastogne. The problem is then getting to Rouen. It's going to take the better part of a day no matter how you do it. If it was me, I'd probably drive back to Brussels, drop the car and train to Rouen. Maybe train to Bayeux. Then pick up a new rental car for the France portion of your stay.

I would take trains from Amsterdam to Bruges and Bruges to Lille (morning departures under 2 hours with a connection at Brussels), pick up a French car in Lille (several major agents at the train station), then drive from Lille to Bastogne (2.5 hours). This doesn't take any longer than train/bus connections from Bruges to Bastogne (4.5-5 hours).

Thanks for the ideas. I'll definitely look into using trains more and then renting a car when needed. I'm sure I'll need one in at least Normandy and the areas around Bastogne.

For the Bastogne portion we also plan to explore the area around Nennig Germany as that's where my grandfathers unit saw heavy fighting during the Bulge. I know there's not much left there regarding the war but walking in his footsteps is of high personal importance. I've also found that the farmhouse where Generals Taylor and McAuliffe made their headquarters is available to stay in. According to the owner, it's where the famous reply of "Nuts" was sent from. It's out in the country away from town. A car will obviously be needed for that portion of the trip.

With Brittany I may not need one as our friends want to show us around. Brest is sister city to my hometown of Denver and the friends we have are heavily involved in that program and come to visit yearly. We take them sightseeing and camping in the mountains every year and I know they're excited to do the same for us when we visit. We've even been offered a free place to stay within the walls of St. Malo.

Obviously I'm in the early stages of planning and the trip isn't till late September but as everyone knows, these come up quicker than it seems initially. Thanks again for the advice, you've given me some good ideas to start with. :)

The one time we did this, picking up a car in Amsterdam and driving to Belgium then up the Rhine into Alsace and then Provence and dropping it in Paris we didn't have to pay the drop fee because they had a Paris car that needed to go home. This was total luck; we were prepared to pay 350 drop fee (this was a while back). What we do is rent cars and drop them in the same country and use trains to cross borders and where we can. We have always used public transport in the Netherlands but used cars in Normandy and rural southern France. You don't want them in cities.