Decide who owns the data before you integrate anything
Most integration pain is not technical. It is two systems that both believe they are the source of truth.
Synchronising customers between a CRM and an ERP sounds like a connector problem. It is a governance problem: when the two disagree, which one is right?
One owner per kind of data
For every entity — customer, product, order, employee — name the system that owns it. Everyone else holds a copy and knows it is a copy. Write this down; it is the most valuable page of architecture you will produce.
Flow in one direction
Bi-directional sync is where weekends go to die. Where two systems genuinely both need to edit, split the fields: this system owns these, that system owns those.
An integration diagram without arrows of ownership is a wish, not a design.