Amsterdam to Bruges to Normandy transportation?

That's a lot of questions. I'll see if I can help with some of them. I've been to all the places you name, repeatedly, but I will say that I have never hired a car in France.

Let's see....

ONE. Any idea where I could rent a car for Normandy?

Conventional wisdom is that the only place in Bayeux is out of town and inconvenient. The same conventional wisdom is that the places in Caen are really easy and convenient, just across from the station.

TWO. Would it be near the French border with Belgium (at a train station)?

You could do that, too. If your previous stop was Bruges it is an easy and short train journey straight to Lille, France which is a large city served by two adjacent stations, Lille Europe and Lille-Flandres, a relatively large station which I am sure will have plenty of hire points. I know that Lille Europe, about 300 metres away, has several desks. The drive from there to Normandy is pretty straightforward.

THREE. Would it be easier for me to return the car at the Caen train station rather than driving to Paris?

Probably. But I don't mind driving into and in Paris, but I also regularly drive in London and learned how to drive in Brooklyn and New York. Others prefer not to drive in any of those places. But your next question seems to indicate you want to go to the airport not the city of Paris?

FOUR. Are there trains that go straight to the airport in Paris?

Not from Caen or Bayeux that I am aware of.

Have you booked your airline tickets yet? If not, I would suggest that you reverse your itinerary to fly into Paris and out of Amsterdam. CDG is fairly easy to fly into, if you are not trying to make a transfer, but it is a mess to fly out of. It is much easier to fly out of Amsterdam.

For a 2008 trip that started in Belgium and ended in France, we took the train to Lille, rented a car there at the station (extracting our Europcar from the confined space in the parking garage was a challenge, and required the utmost care to not ding the car before we'd even gotten it on the road), and drove to Brittany/Normandy, partly in a driving rainstorm. At the end, we turned the car in at the Caen train station and rode the train to Paris. Worked great!

Since the train via Paris is expensive, I would pick up the car at Lille, just inside the French border.