Layer three -
the customer-facing applications, the Clouds. Sales Cloud, Service Cloud, Marketing Cloud, Commerce Cloud, Community Cloud (now Experience Cloud), etc. These are out-of-the-box sets of automations for typical business processes and functions, more or less generic to be applicable in any industry, but because of that, requiring certain customization before use. Salesforce is constantly upgrading its portfolio of applications and introduces the new ones. Together with the powerful backend, this selection of Clouds creates such a unique ecosystem that allows a company to automate all its activities on Salesforce.
Implement it step by step, block by block, never reaching a blocker and never facing a technical need to change the system to something else.