My kids loved Disney, it’s a bit of a battle as an adult/parent but its worth it.
OP, we went many times when the kids where small and we found the resort hotels worth it as you get 1 hour earlier access to the park and you can take a break midday. We bit the bullet and stayed at the Disney one right on the gates for max convenience. It is expensive.
For parks 2 days. There are two now and if it’s busy you will need two days to get round things / go back to favourites, see the parades etc. They do an app now which gives you queuing times so you can plan.
Combining with Paris is a good idea, one or two days to see the major sites and take int he city.
As posted above the train out to the park and indeed to/from Paris is most convenient but may not be the cheapest way vs driving. Have a look for deals combined with park tickets.