I'll give your questions a shot, and if I'm incorrect, I'm sure someone will straighten me out!
I think you'll find that there is only one formal night aboard a 5 night cruise. As I recall, the sister ship to the "Splendour" is the "Legend of the Seas". (Both really great cruises the last time we sailed them) As to the number of restaurants aboard,,,,I simply don't recall. (sound like a politician don't I?) I do remember that the food aboard was excellent and plentiful.
Have a great cruise,