Bonjour.... So sad to be ending my stay but wanted to share a couple of final suggestions/thoughts.
Buy the Museums Pass!!! I can't stress enough how absolutely worth this pass is unless you are going off season or only one museum.
The lines for the major attractions like the Louvre, Saint Chapellle, are REALLY long, think hours and hot and sunny. We literally walked right in and went quickly thru security. Soooo worth it!!!!
Stairs-This may sound ridiculously obvious but.... Be prepared to walk ALOT even with the metro and buses, and up and down many stairs- often tight and uneven ones. There are few elevators/escalators and they are often reserved for the truly handicapped- think wheel chair. Remember this when you're packing your shoes 😉! Lots of cobblestone also....
Local trains- others can address this more as I'm still confused but be aware that you can reserve seats on these trains but don't have to. A little yellow tab by the seat number says its reserved. They are in the same cars as the unreserved seats. Also need to validate them in the yellow boxes before unless you buy them on an app and they validate them electronically,
Toilettes coming from the back of the Eiffel Tower not well marked. Had to ask. They are in the back left corner and are free, unlike the ones at Luxenbourg Gardens which cost .50 euros.
This brings me to coins vs paper money. Don't expect to find machines which make change or an option in the machines to use either. Hard to come by!
Hope this helps!!!!