Make sure you reserve your tickets for the Eiffel Tower in advance if you want to go up and take an elevator, otherwise the wait for the line is super long. You can buy tickets here - https://www.toureiffel.paris/en/rates-opening-times

Also, if you want to go to a lot of Museums and monuments, I recommend the Paris Museum Pass. You can grab one at the airport. The website doesn't work very well, but here is where you can find the information desks in the airport - http://en.parismuseumpass.com/rub-t-points-of-sale-3.htm?cat=3

And here is a list of what it will get you into: https://en.parisinfo.com/what-to-see-in-paris/paris-pass/paris-museum-pass

If you have the pass, many websites will have a way you can reserve your ticket for your visit for free if you read through all the details. For example, the Louvre website lets you buy a specific entry time so you can get in and then you just show that and the Museum Pass when you arrive.