Hi Richard, and welcome to the forums! All good advice for you already, but I'm one to always throw my two cents in!
It sounds like this will be a fairly high-end system (at least in my world where I run a lot of old junk). If you are going to use mobo onboard video, sound, ethernet/wireless... it would have been nice to have shopped your mobo for Linux compatibility first, but it sounds like it's too late for that. You may be fine, or you may have driver issues... only time will tell now. If you are going to add these devices independently, then by all means try to shop for Linux compatibility first. Keep in mind that all this hardware is designed primarily for the Windows market, and it takes awhile for the Linux devs to catch up sometimes, so the latest-greatest hardware is not necessarily a good thing when you're planning to use Linux.
Your new mobo will also have what is called UEFI firmware (also still called by it's old name: BIOS). Out-of-the-box, the UEFI settings are most likely going to be configured for Windows, as I've mentioned already. Some Linux distros will be able to boot up and install without the need to change UEFI settings, and some are not able and require that you go into the Setup and change some items. We encourage you to try several different Linux distros to find what is most comfortable for you and also what is most compatible with your hardware. It may take a little while to find that right balance that suits you.
As others have mentioned, Linux Mint is a very good choice for beginners. It comes in several editions, with the most popular being Cinnamon and MATE (my own favorite is MATE). Both of these resemble a traditional Windows-like desktop, and Mint is well known for automatically finding and configuring your computer's hardware, but it is not perfect either, so you need to keep that in mind. Linux Mint is capable of booting and installing without changing UEFI settings, so it is a very good place for you to start.
If you want to try a "modern" looking desktop, something quite different from the old Windows style, I'd also suggest the standard Ubuntu Linux distro. Linux Mint is based on Ubuntu, and Ubuntu is also very capable of finding/configuring hardware and also booting/installing in UEFI systems. I say the "standard" Ubuntu because it also comes in many editions (including MATE) and this takes it back to a more traditional look. The Ubuntu standard desktop is called GNOME, but you may not see that when you download it.. For a little lingo clarification: when I say "editions"... they may be more properly called "Desktop Environments (DE's)"... as you will soon discover. But also the DE's can vary from one distro to another, and may vary a lot.
There is other Linux lingo you will need to pick up along the way, but you won't learn everything overnight. So take your time, try out some distros on USB, install some of them (and erase them and install others instead). You'll hit some snags, but just ask and we'll try to set you back on the path. With this new system, when you get to the installation phase... choose "Use Entire Disk" for simplicity (and best to avoid encrypting your home folder or the whole drive while you're learning). But I don't want to get too far ahead of you right now either.
Okay, enough from me. Jump in with both feet and have fun!
Cheers