A bill of sale is more akin to a receipt rather than a contract. Since it is such a simple document, there is no way to truly enforce it. If the bill of sale is the only document you use in a transaction, it is best to ensure there is enough detail on it to make the transaction enforceable.
Yes, you need a vehicle bill of sale form in New York for all motor vehicle sales. As the buyer, you'll need it for vehicle registration with the NYS DMV as it serves as proof of ownership. As the seller, it protects you by providing a record of the transaction.