Hi Miriam, writers use fictional names for towns, villages and cities all the time. It allows you to invent details. With small places it avoids the risk of inadvertently alluding to real people or families.
Donna and Laure have given lots of helpful information above.
I think writing about a landscape and culture you've never experienced is a challenge and perhaps only worth the research time if you feel there is no possible alternative setting. It also depends of course on how much of the novel will be set there. The following is my attempt to put you off, meaning that if you're still keen then you'll be enthusiastic enough to put in the time. I don't want to put you off Normandy - it's a wonderful area.
My advice is to read books, especially ones with photos. Novels set in Normandy may be helpful but finding the all-important detail can be a needle in a haystack. If you don't already know the geology then personally I'd start with a book on that. A quick general overview could well be enough. If you know the geology of a place it's much easier to learn how and why it has developed and how it looks, and what grows there.
The internet is invaluable of course but an image search for anywhere often brings up different places without telling you. Having had a quick glance at Normandy images, most of them show glorious sunshine and only tourist destinations. Normandy's weather is changeable. Also you will generally get lots of WW2 images as well. This one for the Rouen tourist board at least shows some of the size of the city, the river and some of the typical Normandy building styles, a mix of timber-framed and stone: Rouen
I've stayed in Normandy a few times and the Wikipedia page looks quite helpful. It mentions the agriculture, a significant feature -- lots of cows and dairy produce, which means a rainy weather pattern. Food with cream, cheese and apples in it. Lots of apple and pear orchards. Huge and frankly bleak areas of arable crops especially on the plateaux where there are also wind turbines and electricity pylons. In the north especially, the local drink is cider not wine, though of course you can buy wine there . Even this site Normandy wine has its main photo of apples, not grapes.
Then there's the local history, people and politics. The history is researchable (there's a lot of it), the rest is more subtle.