There are four coins in the main hallway, and a number of them in the Boos in the yard. Is there anything to gain from them other than health? Do I get anything for collecting them, perhaps in a particular order?
In answer to the title, yes. In answer to the body, no :P
There's nothing special about those coins. They won't trigger lives, secret passageways, or anything else. As I noted on another answer before it was removed, there aren't 100 coins in/around the castle so you can't get a star from them either.