1) Depends on when you go and what you want to see. I would look at the website or get a guidebook. If you want to skip most of Fantasyland and don't like thrill rides it'll be very different compared to wanting to see everything. Time of year does make a difference because the opening hours are so different. But on the assumption you want to do most things and that the parks will be open a fair amount of time, I think you can do both parks in 2 days, but I would take 3 so you can linger and enjoy the atmosphere. The main park is the best themed Disney park I've ever been to (been to WDW and Disneyland). Also, if you want to stay up late for the night time show (a must see in my view) then you may want a slightly later start the next day so more time will help.
2) Stay on site. You can get into the park early and ride certain attractions. The whole park isn't open - so without kids fantasyland may not be attractive to you (though you should see Peter Pan), but Buzz Light year and Hyperspace mountain are usually open, which are fun for adults. At the moment it is 8am-10am in the main park only, but from October that changes to 9am-10am in both parks so you may find more you like in the Studios at that time. I found the extra time very valuable and it was lovely seeing the castle without 10,000 people in front of it! I am not quite sure how the changes will work with traffic flow but if you get to the gates by 8.30/8.45 then you will be able to take advantage of that. It is also so convenient. I think a commute from Paris is quite long and by the time you get up early, navigate the commute and go back it'll be exhausting. On site you can pop back to your hotel for a rest and then go back to the parks. I assume being Canadian you won't be back all the time, so make the most of the few days you have!
3) No opinion on that!
4) To be honest, the food isn't great at DLP and there is not much variety. The Newport Bay Club hotel buffet was solid - good variety at least. You can get excellent pizza and pasta (and other Italian food) in Vapiano - this is in Disney village and is often overlooked given its location. Otherwise, I cannot really comment. I had young kids so we did what was quick and easy and didn't bother looking for higher end food (if it even exists).