Conclusion of a contract with a foreign customer. What subtleties, pitfalls can expect me?

It is necessary to conclude an agreement with a foreign customer, under the agreement I will receive a certain amount of money every month. Since for me this process is new - some questions have appeared:

What should the agreement (contract) look like in case of what it could be, for example, submitted to the bank (as confirmation of the legality of the money I receive from abroad) or as proof of income (I’m not sure if it will be such)?

Interested in, in particular, should there be a copy in Russian? The main clauses of the contract that are important to me, which are the most urgent to pay attention to?

I will be grateful if there are people on the hub who are ready to explain such subtleties.

Thank you in advance.