I am aware that sometimes my comments help to derail some of these discussions, and since you start with a hope to avoid that, I will refrain from responding to any silliness that I may perceive from other people’s comments on here.
In my experience, the best thing to start with is to gain some general knowledge, like how to keep it up to date, reboot it, and all of the things you would need to do over the course of a month on a Windows server. There is a lot of info out there on these things, so your favorite search engine is likely the best place to start, then find something that is easy for you to understand, and bookmark it. I have this one bookmarked: SAM: Learning Linux System Administration | MangoLassi and the author of that is very accessible on this forum.
The first thing I do when I need to find a piece of software similar to something used on Windows that does not have its own Linux version, I search for “alternative to X” where X is the windows only software package. Typically, that leads to sites like these: https://opensource.com/alternatives and https://www.osalt.com/ but there are a number of them. They will help you find Open Source software that is designed to accomplish the same or similar tasks to what you are currently using. Find a few options, never get emotionally invested in any of them, and have your users (target audience whatever it may be) try them all to find one they like best.
Choosing the distro should be an “IT Depends” answer. They are typically pretty similar, but are different enough that one can’t say that CentOS, for example, can handle any and every single use case that you could imagine. If you want to use Debian, but want to install a piece of software that doesn’t have a .deb installation package, then perhaps Debian isn’t the ideal distro for that package. If they have an .rpm install file, CentOS is likely what the developers test on, so you could have better results with that.
My last bit of advice would be to not get caught up trying to figure out what the OS alternatives are missing, but focus your energy more on figuring out if it can still get the job done how you want it to.
As I was typing, I refreshed to see more comments, so I’ll add management can be handled cross platform with tools like Ansible or Salt. I’m going to be learning a bit more about the power of those after my current project, but Humble Bundle did a book deal a short while ago with books for many Open Source utilities, including both of those that I just mentioned.