After studying some basics about n-layer architecture, I face to a new proyect where my database is an ERP and the way to connect with it is via API calls. I can perform queries to obtain data but the only way to insert and update is using the API.
I have to write two applications, a website and a web service. Obviously I cannot just public my ERP API as webservice because a I need to make some restrictions. I'd like to share most of the code, so I have thought writting two presentation layers, using MVC pattern with their own model each one. Functionality might be different, but having shared procedures.
Since bussines logic is mainly done at ERP level, but I still need to implement very simple restrictions, and that persistance layer is based on an API and not directly to a database, what kind of architecture should I use?
Having a domain layer with that very simple business logic seems to overkill for me, and I dont know how if we should implement a data access layer since I don't really have a typical database. All my thoughts are about creating just one layer for this business and data access, but I'd like to know if this is a common pattern I could read or study about.
P.S: I work in a very little team. I still want to separate concepts and make a clean use of layers, but I don't want too much extra work for such a little team. We all will probably work at every layer.