Sales Hub and CRM Hub

Hi,

We are using Dynamics 365 9.1.0.7019 and just got our new instance. We'd like to add Sales Hub but can't find it in Dynamics 365 admin center and found "CRM Hub" is available.

1. Has Sales Hub been replaced by CRM Hub?
2. I can’t hardly find anything on the internet about CRM Hub. But I can see it only has two core entities (Account & Contact), no Sales related entities.
3. Is it true CRM Hub is similar to custom App in the way you add entities to it and customize the way you want?

Thanks

Erin