Salesforce holds the relationship, while orders, invoices, stock and the formal record are usually kept elsewhere. We link it to SAP or Odoo, to the data platform and to public services through MuleSoft or the integration platform you already have. Platform events and Change Data Capture keep the systems aligned, so nobody is caught out by an overnight batch.
Where volumes are high we plan around governor limits from day one: bulk APIs, asynchronous jobs and selective sync rather than copying every record. Our integration and API team looks after the contracts on both sides.