Your scenario isn't a very complicated one so no need to overthink this.
As you do not have the CRM when starting out, there are no restrictions on what you can or may set as the
Ideally you should generate a unique value for each subscriber, and it should not be the Email address or a phone number. Data type should be
text, even if you use a numeric value as the
The only thing to consider is that after connecting Sales Cloud these non-CRM concacts will not synchronise any tracking to Sales Cloud and should not be used together in automations / data extensions together with Sales Cloud records.
Here's what I would recommend:
- Create a unique key for every subscriber as SubscriberKey, data type as text.
- Do your emailings/automations by using the custom SubscriberKey until you get Sales Cloud in place and integrated.
- Import the non-CRM subscribers to Sales Cloud as new records and honor their subscription preferences. This way they will be re-created in Marketing Cloud in synchronised data extension as new lead/contact records with Sales Cloud Contact/Lead ID's.
- Export send history for the non-CRM contacts from Marketing Cloud.
- Delete the non-CRM contacts from Marketing Cloud.
This way you'll end up with a clean database in Marketing Cloud where your contacts are properly recognized by their Salesforce record ID's and history tracking is synchronising back to Sales Cloud.