Hi mohan_infosec,
1 & 3: Microsoft Defender for Endpoint (for servers) is not just EDR, see Microsoft Defender for Endpoint | Microsoft Security for an overview. The unified solution replaces the previous one, no longer uses a log analytics workspace or the agent for it (regardless of how you onboard), and, adds Windows Defender Antivirus as well as EDR to Windows Server 2012 R2. On Windows Server 2016 Defender AV is already built in and it only installs the EDR sensor; on Windows Server 2019 and later both are built in.
2 & 4: There are two ways to get Microsoft Defender for Endpoint functionality for your servers and to make it super clear they each have a pay and onboard step that are tied together. One is through an Azure subscription (pay) and Microsoft Defender for Cloud (onboard); the other is through purchasing (pay) a specific subscription license in your license agreement and by onboarding (onboard) directly to security.microsoft.com.
1. Using the Microsoft Defender for Endpoint license included with Microsoft Defender for Cloud | Microsoft Docs - Microsoft Defender for Cloud includes a Microsoft Defender for Endpoint license for your servers (and much more functionality on top of this!!!). Billing is performed pay-as-you-go through your Azure subscription (pay), onboarding is performed using Microsoft Defender for Cloud (onboard) and it does use a log analytics workspace even if this is not used by the agent (note that the topic of this blog, the preview, is not yet integrated into Microsoft Defender for Cloud).
2. There is also a Microsoft Defender for Endpoint - server standalone license (1 license per server). This is what is required to onboard servers directly to your Microsoft Defender for Endpoint environment (security.microsoft.com, onboard) without going through Microsoft Defender for Cloud. These licenses should be purchased (pay) through a licensing agreement, please reach out to your Microsoft rep.