There are religious services and a chaplain on board, so you certainly will be able to get your Easter service in.
Tipping is optional; we did because we appreciated how our servers and cabin steward went out on a limb.
We liked the L'Approdo restaurant, because it was cosier, but we heard no complaints from Caravelle. We enjoyed dinner in Caravelle at the captain's table on the second Gala night, but who can judge overall service from eating at the captain's table? I certainly don't think the wait staff is going to neglect THAT table!
While your dinner seating is constant, you can choose to eat at any table in any of the restaurants for breakfast and lunch. Below is the link to our cruise photos if you'd like to see them; as you can see, we had lots of fun. (You'll probably have to copy and paste in the address bar.)