In my situation, my company services many types of customers. Almost every customer requires their own Business Logic. Of course, there will be a base layer that all business logic should inherit from. However, I'm going back and forth on architecting this--either in one dll for all customers or one dll for each.

My biggest point of contention deals with upgrading the software. We have about 12 data entry personnel that work with 20 companies and it's critical that they have little down time. My concern is that if I deploy everything in one dll, I could introduce a bug in company A's logic while only intending to update Company B's logic. I believe I could reduce the risk if each company's logic had their own dll, so then, I could deploy Company B's update w/o harming Company A's. -- I will be the only one supporting this.

That said, this also seems like a nightmare to manage 20 different .dll's -- that's for the BLL alone. I also need to create a View layer and ViewModel layer. So, potentially, I could have 20 (companies) * 3 (layers) which would equate to 60 .dll's.

Thank You.