How do opportunities/activities relate to dealership employees?

How many characters are allowed in the body of the email.

We do not see any dealerId. How do we know who (dealers) owns those opportunities? I assume one dealer per subscription-id?

Search → According to the API, we cannot search by name, phone number, email, address, etc., but can only do it by Customer ID. Is that correct? Ideally we can pull data without knowing the customer ID. Is that possible?