Yes, you can switch your license from one domain to another. You can learn more about it from here.
Please see this section of the documentation to learn how to obtain the HubSpot API key..
No, you do not have to create blank forms every time; instead, you can use any existing forms. Simply use the HubSpot Integration processor.
The free edition only allows you to sync first name, last name, and email address. To sync more user data such as an address, city, country, phone number, etc., you must upgrade to the pro version.
Yes. Caldera Forms plugin must be installed and activated.
The user data can be found on the Contacts page of HubSpot