These are correct:
It is a five-star hotel.
The hotel has five stars.
When used as an adjective, nouns are normal singular: a ten-minute coffee break, a three-day trek. Most people do NOT say '5 stars hotel'.
These are correct:
It is a five-star hotel.
The hotel has five stars.
When used as an adjective, nouns are normal singular: a ten-minute coffee break, a three-day trek. Most people do NOT say '5 stars hotel'.