I have a physical server that has windows server 2008 r2 and has Active Directory Domain role installed on it. Now I have a new physical server (HP ML350 Gen9) and I want to install Windows Server on it and make it work as our production server (for our shared files and folders, sql server databases, web services ...) but I cannot decide which windows server version to purchase (2012 r2 vs 2016) and what license (Standard vs DataCenter). My company has currently 22 employees that will be on the network, the server will be managed by one administrator and will be accessed through a single user with RDP. I'm not expert at the different versions and licenses of windows server, and I do not understand how should I decide what to purchase for what I need. And what are CALs? Since in their website I see the following for Standard edition: "The licensing for Standard edition will continue to be processor plus CAL, with each license covering up to two physical processors on a single server, just like Datacenter edition." And similar description for DataCenter edition.
Please help me understand a bit about it and help me in my decision.