How do I know what my requirements are? Well, if internal processes have been defined, this should be an easy question to answer. You should start with the most important and frequent processes, and move on to the least important or infrequent processes. The important and frequent ones should be handled by the ERP, while the least important and infrequent processes may or may not be handled by the ERP, depending on your goals and the budget for the implementation.
Talk to the consultants who will be implementing Microsoft Dynamics NAV or Microsoft Dynamics 365 Business Central for your organization. Tell them what your process looks like, who is involved in it, what information is required, and so on. They will tell you how this specific process is resolved in these ERP systems.
If the way these ERP systems handle the process matches the way you handle the process, you've...