Do you have to use the service account email address that is given to you or can you use an existing email address that is connected to the accounts you have access to?
service account credentials are a specific type of credentials created on google cloud console and are used to denote your application. Service accounts also allow for pre-authorized Access to private under data by in the case of google analytics adding the service account email address as a user in google analytics.
No you can't use a standard gmail user account as a service account.
You would need to use oauth2 to request consent of the owner or user of the google analytics account to access it.