Что интересно, правы оказались те, кто ответил, что регистрироваться нужно в России.
Я написал в Upwork и мне ответили, что по их правилам:
> You can incorporate your Agency to the company account which means the agency's location can be different from the Agency Freelancers location, However, please note that the payment methods will depend on the Agency owners location. That means, you will not be able to use your company bank account that's located in another country to withdraw from your Agency.
Такие дела.
