A restaurant patron is a person who is eating in the restaurant. They "patronize" the restaurant.
Anything proper to the restaurant itself is the restaurant's, as is anything owned by the restaurant owner that is in service to the restaurant's function.
at a restaurant = in einem Restaurant
An international restaurant is a restaurant in a different country
How a restaurant is called = Comment s'appelle un restaurant. A restaurant is called X = Un restaurant s'appelle X
to eat at a restaurant is "manger au restaurant" in French.
No, it is not. Restaurant is a noun.