I’ve been twice and really liked it. There is a LOT to see, and the food is amazing; visiting a food market is a must. To answer your questions:
1) You will have no issues. TBH, the French can be kind of blunt to the point of being rude, and I tend to scrap all attempts to speak French (and TBF I’m not THAT bad) fairly quickly, as they will simply respond in English. Learn some basics, but really that’s all you need; that, and an understanding of how the Metro works (we found it confusing at first but it’s actually REALLY simple)
2) My top things to do are:
Visit a food market; if you travel when it’s warm, there are some lovely parks you can picnic in.
Arc du Triomphe
Berthillons ice-cream parlour (located near the Notre Dame; the ice-cream and sorbets are UNBELIEVABLE and the streets round the shop are very pretty with lots of beautiful buildings and nice shops (like unusual jewellery shops, florists, patisseries, etc)
Take a cruise down the Seine; there are several options for this inc lunch and dinner cruises, or just your basic tourist cruise. Great for seeing the city from a different perspective and the tour/guided ones have a commentary which is really interesting and informative
I also enjoyed the Picasso museum, as I like Picasso, and the Rodin museum is worth a look to; the gardens are particularly lovely. The Museum of Modern Art at the Pompidou centre is also worth a look if you’re into modern art (not everyone’s cup of tea though!)
The Eiffel Tower is also a must; we took the lift, you can walk if you’re brave!
The Louvre is also a must, though I admit I’ve not been myself as I didn’t have the time on either trip (one was 4 nights and one just 1 night, and we had other priorities)
Finally, the shopping is also worth checking out; they have a couple of big department stores like Galeries Lafayette, lots of chic high-end designer shops around Faubourg Saint-Honore, and art and quirkier items in the Marais area.
3) I’m afraid I haven’t been; sorry.