If you switch your arrival day and go to Les Invalides for the tomb first and have a visit time for the Eiffel Tower afterwards. The museum closes earlier than the Tower.
Note if at all interested in climbing the Notre Dame tower, it's 424 winding steps up and 425 winding steps down.
Thursday, you have a nice mix. If strolling on the Île de la Cité, be sure to cross the bridge to the Île Saint Louis and stroll around, too. Like Pam, I'm not a fan of the catacombs. I was there in 1973 when we had to carry our own flashlights. Instead, I'd spend the time relaxing in the Luxembourg Gardens.
The Louvre is a good choice is you know what you want to see. The problem is that it contains several museums in one, which can be either convenient or confusing. You can see the Egyptian collection, Hammurabi's Code and multiple early civilization objects, Greece, Rome, a section on Northern European painting, French painting from the 13C to 1875, Italian from the primitifs on, Spanish masters, precious objects, jewels, Napoléon the Third's apartments... There are hundreds of masterpieces, much more than the big three ladies, Mona Lisa, Venus de Milo, and Winged Victory and Michelangelo's Slaves. You could study online, choose highlights and then try to see them.
As Slate said, the Musée d'Orsay is much smaller, more limited to a short time period, but IMHO, a doable, pleasant museum with interesting sculptures on the ground floor, interesting paintings on the ground floor marking the period of technological and social change which led to the period in art that we call modern. Then the final breakthrough to modernity is on the 5th floor, the floor most people run to when they get into the building because it has the Impressionists and their colorful paintings of an easy lifestyle and the post-Impressionists. This is an easy museum to navigate, has both a casual restaurant and a white-tablecloth restaurant.
The third museum in the national museum sequence is the National Museum of Modern Art, which begins with 1905 and cubism. It's in the Pompidou Center, currently under renovation.