Before you book anything, call the office to make sure the itinerary is still the same as listed. It NORMALLY has the same things on the same days but there are occasional diversions due to circumstances in a location. I'd also ask what time they have tickets for the Louvre tour just so you know the timing in case you want to do the Moulin Rouge that night.
You have free afternoons on Day 2 and Day 6 so you could do the Catacombs on those afternoons. You could do the Moulin Rouge on Day 2 or Day 3 if you want to skip the Seine Cruise or Day 4.
I'd not do the Moulin Rouge on Day 5 when you go to Versailles. When I did this tour we did the palace together and then did the gardens on our own and were given RER tickets to get back to Paris on our own (very easy). It's a long day and I was tired!
This is an excellent tour! I learned so much and it really increased my comfort level in Paris. Downside? Uh.....well, I can't get enough of Paris and have to keep going back!