What are the key considerations when setting up Marketing Cloud for a new business unit or new client org?

A structured MC setup checklist for a new BU or client org includes:
1. Account structure: Determine BU hierarchy — single BU, Enterprise with child BUs, or separate Enterprise accounts per brand.
2. Authentication: Provision SAP (private domain, dedicated IP, SPF/DKIM, RMM). Configure DNS records and verify in MC Setup.
3. IP warming: Plan a 4–6 week warming schedule before launching full-volume sends. Identify engaged segments for initial sends.
4. Users and roles: Create user accounts with least-privilege roles. Configure SSO if the client uses Salesforce CRM or an IdP.
5. Data model: Set up Contact Builder attribute groups and sendable DEs. Define subscriber key convention.
6. Compliance: Configure publication lists, preference centre CloudPage, suppression lists, and GDPR consent tracking DEs.
7. Automation: Set up SFTP access, import automations for CRM data, and data retention policies on import DEs.
8. API access: Create Installed Package with minimal required scopes. Restrict to known IP ranges. Document client_id/client_secret in a secrets manager.