Defender for Endpoint P2 Licensing

Hello, we are in the process of implementing Defender to replace Cylance which is going EOL soon. We use Citrix and have 100 Citrix application servers in our enviroment and over 1200 users that access Citrix applications. We also have 500 Windows servers that we want to onboard defender P2. The way I understand it and please correct me if I am wrong is, the security.microsoft.com is where you onboard servers no matter what. 

1. Are P2 licenses, licensed per user or per device?
2. For servers only, not Windows PC's, do we license P2 to servers or to users? 
3. Can anyone elaborate the difference between intune.microsoft.com and security.microsoft.com and what we use for server management, onboarding and users. 
4. I am only concerned with server management in this thread. 
5. Earlier today I enabled our Microsoft Defender for Endpoint P2 Trial and it says right away to assign the licenses to users on the users page. This takes me to the admin.microsoft.com site and shows all the licenses. I then see Microsoft Defender for Endpoint P2 and the 25 trial licenses. 
6. Why do I assign licenses to users? Referring to servers here. 
7. I really could use some help in understanding how this all inter connects, admin.microsoft.com vs intune.microsoft.com vs security.microsoft.com etc.