Hi AdmWombat,
1.Opportunity entities are associated with leads and not directly with contacts,
so using Dataset Configuration to synchronize entities is an effective way to do this if the segment attributes already in place don't meet your needs.
2.According to the official documentation, it is recommended that you only add the entities you need, as synchronization occurs frequently, and it takes up your storage space and processing time.
That's why there are only three entities added by the system by default (Contacts, Accounts and Events).
About storage space and processing time:
1)The dataverse has a limited amount of storage space, and once it is exceeded you can only delete files you don't use often (which are often attachments to emails) or buy more storage space.
2)Compared to storage space, response time is more important. If you add too many entities, you will undoubtedly increase your wait time, which will affect your experience.
Best Regards,
Haig Liu