It’s really up to you. If you want to just dash into the Louvre, run in and see the Mona Lisa, then go do something else, you could probably do the Arc de Triumph, Champ Elysees, Hotel de Ville, Notre Dame, Place de la Concorde, the Tuileries and the Louvre all in one day.
The two closest to each other are the Louvre and Notre Dame.

Versailles is one full day.

Go to the Pompidou Center then have a street picnic outside afterword.

Get a Mapeasy map or app.

Sweetheart, you’re overplanning. And as Cil advised in the Rome thread (and you didn’t need to start 5 different threads), just look at a map. You can walk from Notre Dame Cathedral, to Sainte Chapelle, Hotel de Ville, and the Louvre, then through Tuileries garden (which is just a lovely park) to Place de la Concorde. And honestly? I’ve lived in Paris and gone back many times, and never been to Sainte Chapelle. Don’t kill yourself if you miss something.

And don’t kill yourself for tourist traps. If there’s a line to go up the bell tower at Notre Dame, don’t do it. Not that lines aren’t always worth it (the Catacombes are worth it)…but do you really need to go up the bell tower? There’s other great views of the city, as I’ll mention below.

Hotel de Ville, btw, is just city hall, and that’s what “hotel de ville” actually means in French. City hall. It’s a gorgeous building, and there’s a nice square in front of it. You’ll catch a glimpse of it for a few minutes as you’re walking (or maybe stop for 10 minutes and take pictures), and then you’ll move on.

The Eiffel Tower is sort of an outlying attraction, relative to the rest, so take the metro to get there. Unless you really need to go up (and the view that high up isn’t that great…you can get the same exact view of Paris from Tour Montparnasse…but you’re probably gonna want to go up the ET just to say that you did), I wouldn’t go up. I’d just buy some wine, bread, cheese, and foie gras from a supermarket…go to Trocadéro park right before dusk and wait until the top of the hour to watch the tower sparkle. Every hour at the top of the hour [during the nighttime hours] for about 5-10 minutes, the floodlights shut off, and the sparkling lights turn on…and Trocadéro is the best spot to view this from. It’s quite the sight, especially if you can be there around dusk, when the sky isn’t quite black yet. Then, I would head across the river, pass underneath the tower, and have a picnic on the other side of the tower, on the Champ de Mars park, with the bread/cheese/wine we bought earlier in the day. Done this countless times. Welcome to Paris.

Another great place for a dusk-time picnic? The Pont des Arts bridge.

Don’t kill yourself trying to “efficiently” see the city. This is one of the most aesthetically-planned cities in the world, there’s lovely architecture everywhere. Don’t overlook the actual city itself, as you’re hurrying to see the “sights”. The Latin Quarter is nice, and loud at night. My personal favorite areas of the city are everything between Montparnasse (which is a complex that includes a train station, mall, and skyscraper) and the river, including the areas around Luxembourg Garden. All walkable. Just walk around. You get lost? Find the nearest Metro station, and you’re set. Another neat neighborhood to check out is the Marais.

Sacré Coeur church is on Montmartre hill. I would spend an afternoon exploring that lovely neighborhood. Great view of the city from Sacré Coeur, btw. And it’s free, and no lines!

Versailles is a suburb of Paris. It’s not in the city. Make that a half-day trip from the city. Take the RER commuter train in the early morning. Be back by the afternoon.

The Louvre is massive. If you want to go inside, I honestly wouldn’t spend too much time in there, or you’ll miss Paris. Pick one or a few places/time periods that you like (Italian Renaissance? Flemish art? Greek and Roman sculptures?) and find them, and leave. Don’t get lost in there for hours. If you’re not interested in going inside, definitely check out the outside including its courtyards. If you want 19th century French art (such as the Impressionists), you’ll want to head over to the Musée d’Orsay. That’s a much smaller museum than the Louvre, thankfully.

Centre Pompidou: I don’t really care for the building itself (although I think the side facing the square is nicer than the side facing Rue Beaubourg…but not one of Renzo Piano’s best works, IMO). But the view from the top floor is one of the best views in the city (http://www.centrepom…). It’s located in a cool, gentrifying part of the city…there’s a little bit of a punk/student feel to it. The Marais is nearby, which is traditionally Jewish, but has become artsy and also the city’s gay district…and the building stock in the Marais is generally older than most of the rest of city which was built in the mid-to-late 19th century.