Always start a conversation in French, no matter how limited your French is. Locals will always be glad you tried. In Paris, most shopkeepers speak at least a little English, especially at monuments visited by lots of tourists. It’s when you someplace in France that’s not Paris that way fewer people speak English (and why should they have to?).
For going shopping, you should be good with limited French, though you may want to look up phrases like ‘Does this come in a bigger size?’ and anything else you might think would come in useful.
If you want tap water in a restaurant, ask for ‘une carafe d’eau’ and you will get a pitcher of free water! If you just ask for water, they will give you bottled, and you will have to pay for it!
Something else handy you can pick up is a ‘Pariscope.’ You can buy one at any ‘Presse’ stand (and there’s one on every corner, and quite a few in the middle of the street as well… apparently Parisians don’t get subscriptions to newspapers) for only a few cents. It’s (in French) a listing of museum and other monument hours, prices, and locations, as well as upcoming events, movie times and places, restaurants, and more! If you have a bit of French it could come in very handy. A new one comes out I think it’s every Wednesday.
I would check the websites of the attractions you wish to visit to see if they have wheelchair accessibility. Pretty sure the Arc de Triomphe is going to be out of the question, as well as likely the Eiffel Tower and Sainte Chapelle as well.
There would still be lots of do-able attractions, such as the Louvre, the Musée d’Orsay, and Notre Dame de Paris.
There are cobbled streets and other non-smooth surfaces such as dirt that may make some places less accessible, but I’m sure a determined person could still see a fair amount of the city.