Have been to Paris a bunch -- some personal, some business.
My recommendation for the Louvre -- find a guide who can get you in and is knowledgeable enough to lead a tour. I can probably dig up some names. It's a mob scene but well worth going to if you can get some help. Also, don't ignore the building, which is fantastic. Also, bring binoculars if you have them. in order to see the architectural detail there and elsewhere.
Don't miss Musee d'Orsay. It's where the Impressionists and Post-Impressionists are displayed. Picasso is also well worth seeing, and it's in the Marais, isn't it, where you can walk around. The museum is his personal collection -- many of his most famous works are in museums elsewhere.
The last time I was in Paris was just after the Brexit vote in Britain, and as I was walking around the neighborhoods with those handsome apartment buildings, I was thinking about all those rich bankers fleeing London and moving to Paris as the international banking center shifted location in order to remain in the EU.
Also, it's worth getting a list of small restaurants that are au courant -- the list changes pretty often. Many of them are in side streets or in residential neighborhoods.
Sage Grouse
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'When I got on the bus for my first road game at Duke, I saw that every player was carrying textbooks or laptops. I coached in the SEC for 25 years, and I had never seen that before, not even once.' - David Cutcliffe to Duke alumni in Washington, DC, June 2013