Paris Itinerary - 4 Days in Paris

Paris Pass is an awful deal. Get the Museum Pass.
For transport, look at the Navigo Decouverte. 22.80 EUR plus 5 EUR initial fee and a 1" by 1 1/4" passport type photo, which could be a selfie or a photo copy of your passport photo reduced to the right size. It might be borderline price-wise with just buying 10 packs of t+ tickets and separate tickets for Versailles, but it is convenient as all-get-out for getting around Paris, it will include transport to Versailles, and you can even use it to get to Orly if you are willing to take the short bus ride from Pont de Rungis RER station.

Yes, the Museum Pass is the one to get, if you get one. But only two of your listed places are covered by the pass (Versailles and Louvre), so you might want to calculate whether it would be a good buy. To see just those two sights, you'd want the two-day pass, visiting each on consecutive days. The pass would get you into many other worthwhile sights, skipping the ticket-buying lines, so it might still be a good investment.

Your four days are ample for what you most want to see. The Arc de Triomphe takes little time, even if you climb to the top for the view. Notre Dame can take a little time or a lot depending on your interest. Climbing up the towers will take longer (covered by Museum Pass) if you want to do that. See the "Explore Europe" link above for more ideas about things to see in Paris. Give Versailles a full day, and consider that the Louvre is open at least one of the evenings you'll be there.

A river cruise is fun and a good introduction to the city. I like the Vedettes du Pont Neuf, but there are others leaving from near the Eiffel Tower. I've never done a nighttime cruise but I'm sure it would be fine. Sunset will be pretty late in late May and you may want to do this in the daytime. I'd recommend against a dinner cruise because it focuses you on your dinner along with the scenery you're passing. You can eat anywhere, after all. But some travelers love the dinner cruises, so who knows?

Arc de Triomphe is also covered ny Paris Museum Pass. Do you have Eiffel Tower tickets already, or do you plan to 1) stand in line to go up the tower or 2) look at it from the bottom, across the river and from other sites (we have done the latter on past trips)

It depends where you will be staying (which arr.). I like to have 2 things planned per day, and divide these by area. So I might do the Louvre and Arc in one day (Louvre in the morning. then lunch, then Arc, also bc the Arc is outside and you will have been inside so long in the Louvre), or Notre Dame and I suggest Saint Chapelle 2 blocks away and stunning - you could also walk around the two islands on this day. I like to walk everywhere, and unless a site is quite outlying from where I am staying (like Pere Lachaise cemetery, or the Catacombs) I mostly walk, because I get to know the city so well and see so many small things I would miss taking the metro (all the 1 block parks with beautiful statues, or churches, for example), therefore, I plan my itinerary by area. So last summer we stayed in the St. Germain area and one day walked from there through Luxembourg gardens to the Eiffel tower, then over to the Army museum (Napolean's tomb), then back to St. Germain along the river). So look at where you are staying in relation to various sites (which you can see just on a google map of the city), and imagine which places will take linger or more energy (the Louvre will take a lot, Notre Dame less, etc), and try to chunk your visits by area.
I have to put in a plug for the Orsay museum, and Saint Chapelle.

Thanks all.your guidance is much appreciated.We are staying in the 7 Arrd. Viewing the Eiffel from the ground.during the day as well as at night.

Don

We've taken Seine cruises with several with different companies. Les Vedettes du Pont Neuf is by far the best in our book. Don't book ahead because you never know what the weather will do. Just show up. The advanced tickets don't save that much as I recall. Do it after sunset as the lights of the city are great - especially the Eifel Tower.