Other posters have advised you about the "skip the line" tours. No one skips the security lines. At the Eiffel Tower there is one elevator going to the top. Your tour guide won't be able to get you ahead of the people waiting for the elevator. You will have to wait in the same long line as do others. The lines the tours skip are for ticket purchases. I assume they have relieved you of reserving your time.
Re Champs Elysees, it is a long walk past chain stores and restaurants. The view looking down it from the Arc de Triomph to the Place de la Concorde is terrific, but walking there is not like it used to be in the 50's and 60's. Maybe tweak this activity. For a kind of classic Paris walk, I like stroling along the left bank of the Seine, past the bouquinistes, stopping at a cafe along the way, from the Pont de l"Archeveche to the Pont Des Arts. You get the classic and fantastic rear view of Notre Dame, the bookstalls, many cafes, and can cross the river near the Louvre and Tuilleries. Just a thought.
Re Versailles...yes it is a bucket list item, but unless you can get a really early reserved time and visit, say, the Hall of Mirrors first thing, there will be HUGE crowds. I always plan on this being a full day because the grounds are so large, as is the palace. The train to and from it are easy. To save some of the line waiting, buy the King's Apartments tour when you reserve your time. That should cut down a little on the waiting. However, with your short time in Paris, I sincerely suggest tabling this for another trip. (Of course, that's easy for those of us who have been there to say, so feel free to ignore this suggestion.) And I have heard too many complaints about Viator tours to ever want to use them. But that's me.
One thing we sometimes do is walk around the Eiffel Tower and admire it from the Champs de Mars, then walk to the Invalides (army museum) and see Napoleon's tomb (plus suits of armor if you are interested), then walk to the Rodin Museum (one of my absolute favorites) and admire the sculptures in the garden, especially. The cafe there has some nice food for lunch. From there you can walk to the beautiful Pont Alexandre III, then across to the Grand Palais, then to the Arc de Triomphe. This is probably too much for one day, actually, but is a nice route to work around.
jeanm is right about the Seine cruise. Have your meal before or after so you can get the most from the boat ride. We like to sit up top on Vedettes de Pont Neuf. Inexpensive, well narrated, about one hour.
Museums....too many to choose from. It depends on what you are interested in. The Rodin, Cluny, Orsay are my favorites in Paris, but go with what attracts and interests you.
The riches of Paris await you! Enjoy! Amusez-vous ien!