After a few days in Bilbao, my husband and are heading to Rouen so that I can visit some places from childhood memories of visiting my mother’s family. We’ll use Rouen as a base for 4 days to go to Les Andelys, Les Trois Lac, Honfleur, Omaha Beaches, Buchy area. Then 3 nights in Sant-Malo for Bayeux and Mont Saint Michel. From there two nights on Jersey, because why not. How’s that for an itinerary. Please let me know. Starting in Rouen on Sept 1.
The D-Day beaches, including Omaha Beach, are best visited from a base in Bayeux or elsewhere in that area. Rouen is lovely, but it isn't well positioned for visiting D-Day sites I recommend at least a one-day, guided tour of invasion sites so you know what you're looking at, unless one of you is an expert on the invasion. I was very happy with my Overlord Tour, but there are other options. Seeing Bayeux will be easier if you're staying there rather than backtracking from St-Malo.
Jersey is absolutely worth visiting. I spent 4 or 5 days there myself in 2017 and could have happily stayed longer. The issue with trips to the Channel Islands--assuming you're planning to take a ferry--is that the boats can be canceled, leaving you in a tough spot. I've booked 5 journeys between St-Malo, the Channel Islands and southern England. Two of those ferry trips were canceled, one of them for 3 days in a row. Both trips fell between May and September, so no winter weather was involved. I'd definitely not be willing risk being on one of the islands the day before I was due to fly back to the US or Canada. If that's not the way your itinerary is laid out (or if you're prepared to take the financial hit that could result from being marooned on Jersey), go for it. However, I'd certainly want more than 2 nights on the island, given the challenges of getting there.
The drive from Rouen to Bayeux is close to 3 hours, and the beaches are further out. That's not really the best base unless you really like the drive. I'd look at St Lo as a base if not Bayeux.
I love Rouen, but if you have a car make sure you get a parking place with your lodging. If not plan to add a minimum of 30 minutes looking for a space every time you drive somewhere.