One who collects coins as hobby :
One who collects coins as hobby : Correct Answer Numismatist
One word substitute is NumismatistPhilatelist: a person who collects or studies stamps.
Ornithologist: a person who studies or is an expert on birds.
Statistician: an expert in the preparation and analysis of statistics.
Numismatist: someone who studies or collects coins, paper money, or medals.