The course is in 6 sections, so I'll separate them by parts. I do have Windows Server experience, and 2019 is new to me, though the general idea is the same.
The first relevant video opens with
"I was speaking recently with a network administrator for a global company. He told me that his IT infrastructure was out of date because his Windows Servers were a version or two behind the newest thing from Microsoft."
Just because you can upgrade doesn't mean you should! If your stuff works (well), it works. If new features help your business, or have the possibility for your business to 'grow' into them then sure, upgrade. But there's no need to keep up with the Jones or Gates.
💭 Consider the role of Active Directory and how it will work with your new servers.
💭 In-place upgrades keep the settings and configurations while pushing it to a new version of Server. Roles may or may not transfer, or need to be configured differently. Use SMIG tools to port old settings to a new server.
💭 Some roles require more resources than others. Some done. Consider coexisting of less powerful roles on the same server.
💭 Windows Defender on Server 2019 has Ransomware protection. It was a challenge to keep machines current, so ATP was invented to centralizing the task of interpreting data, that you access via a web based portal (via Azure, so subscription needed), with scanners on each machine.
💭 DNS also keeps track of things in Active Directory, and DHCP helps it keep track of devices that have received IP addresses with IP Address Management Server.