Have 2016 Essentials running ok. Have reached the limit of 25 Users. I have read and understand the process to move to 2016 Standard. Most of my users use the Remote Desktop to connect to their PCs in the office. Some also work directly on the PC in the office.
Two questions: What CALS will I need to keep both operations going.? Will the Windows Server Dashboard still be available once the upgrade is done?
Just normal Windows Server 2016 Cals, nothing special. The Standard version also comes with the Essentials Experience role just does not have the limitations.
There are two types of CALS, Local User CALs and Remote Desktop User CALs. Which would I need.
Certainly not RDP Cals. You need either Per User or Per Device, see https://www.microsoft.com/en-us/licensing/product-licensing/client-access-license
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I am fairly sure you can change the product ID to a standard windows 2016 licence: