Yes there are 2 parks and yes getting a park hopper for 1 day is worth it. The Studios park is located beside the main park, takes about 7 minutes walk from Main Street Train Station to the entrance to The Studios. The Studios is really a half day park anyway. The 2 unique to Disneyland Paris rides you don't want to miss are Ratatouille and Crushes Coaster.
Ratatouille is a trackless 4D dark ride, do a Google search for more information.
Crushes Coaster is a rollercoaster Disney style.
You could park hope for about 3 hours to do these 2