To address your questions partly, I will try to answer some of your questions with what I have known about DNA Center.
1. There are many addition packages available for Automation & Assurance. You can either download them individually and upload into DNAC or update it directly inside your DNAC. Since you are using your Cisco IDs to start using your DNA Center, the charges may be applicable depending on the package you download.
2. To answer you second question, yes Path Trace and Easy-Qos are available inside the DNAC. It is said that the APIC-EM features are embedded into Cisco DNAC, so you will be able to avail most of the features that were available in APIC-EM 1.6.X which was the last version released. Additionally there are many new features in DNAC adding to the APIC-EM features. They call the DNA Center as APIC-EM 2.X version.
3. The hardware platforms supported in APIC-EM differ with that of DNA Center. To know more in detail about the products that are supported by Cisco DNAC, you can follow the link https://www.cisco.com/c/en/us/solutions/collateral/enterprise-networks/software-defined-access/guide-c07-739242.pdf
4. We don't need to deploy a site like we do in APIC-EM, deleting and re-provisioning a site. We can change the DHCP/DNS and AAA Servers by simple steps.
For more information regarding the DNAC, refer the SD-Access CVD https://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/Campus/CVD-Software-Defined-Access-Design-Guide-2018MAR.pdf
Hope this Helps!