Financial institutions have been progressively challenged by being linked to a network of various internal and external systems through different and complex protocols. The way to manage this challenge is exploiting application-specific gateways known as financial gateways. However, the complexities of switch protocols as well as the variety of internal and external systems make the design of financial gateways quite complicated. This paper briefly summarizes the challenges of building family of financial gateway systems and introduces a systematic approach to design and implement them with "Domain Specific Kit" abstraction. This abstraction can separate system design concerns properly, isolate them in discrete building blocks, and finally compose them by means of a structured choreography model. The approach has been implemented within the context of OCTOPODA project and experimented in real life cases. The paper also presents and discusses the results of this experimentation.