Stella,
I'm wading into the discussion a bit late, but have a few comments. Your initial Itinerary wore me out just reading it; it's FAR too ambitious! In reading through some of your subsequent posts, it's good to see that you're going to slow it down a bit.
How are you planning to get from Paris to Rome? Is that already arranged?
If you're traveling from NYC, the jet lag likely won't be as bad as those of us on the west coast have to deal with, but it will likely still be somewhat of an issue. You may want to allow some time at the beginning to get up to "touring speed".
What are you most interested in seeing in the Louvre? The Mona Lisa is usually at the top of the list for most people, and that's located in the Denon Wing. Be sure to wear a Money Belt and be vigilant for pickpockets especially in that part of the Museum, as they WILL be operating there. The "scrum" in front of the painting is often VERY tightly packed, which provides optimum conditions for pickpockets. However I should add that when I was there in June, I only experienced some "probing" but didn't lose anything.
Regarding the "quick lunch by Orsay", you could also have lunch inside the Orsay. There's a beautiful and elegant formal dining room on the second floor (white linens, that sort of thing) and a Cafeteria on the top floor. The Orsay is one of my favourites, and I could easily spend four hours or more there.
To streamline your planning, you might try listing all the places you want to see in Paris (and Rome) in order of priority. Try to fit in as many as you can on a relaxed touring schedule. Any that are left over, you can see on the next visit (that's the method I normally use).
Where are you planning to buy your Paris Museum Pass? They're sold in the airports, so it's very easy to pick one up when you arrive.
I definitely agree with a previous suggestion to pick up a copy of the Pocket Paris and Pocket Rome Guidebooks (although not sure there will be time to order them in?). You may be able to find copies at larger book stores in your area.
One important point to mention..... there are some potentially expensive "caveats" when using public transit in Rome (and Italy). If you need further information on that, send me a PM and I'll provide my usual "boilerplate" on the subject.
I'm assuming your trip is coming up very shortly, so you'll have to get the planning sorted fairly quickly.
Happy travels!