Are you sure the Gigabyte z490 Vision G or Asus Strix ROG z490 will work with Mojave ?
So you do have 32-bit apps…
And you could have answered yourself the question about the OS version to run.
Note that running Mojave has consequences for the GPU you could use: No Navi/Big Navi cards, you're limited to Vega and Polaris.
In this thread you have suggestions for three well-supported Z490 motherboards. Four with the Z490 Vision D, if you can source one. At this point it really is up to you to check their
detailed specifications (including any fine print about line sharing…) and how you could fit in all your hardware requirements—which stretch a consumer platform to its limits, and possibly a little bit beyond. Then check the build threads here for Mojave support, or any other feature you're interested in.
Please carefully review and sort out your wish list (required/would be nice/could be nice/could do without), it will help you—and help us help you if you care to share the result.
If Mojave support is critical, and you want certainty that Mojave will run without issue and without extra hassle, then you should actually look at Z390 and 9th generation CPUs.
What do you think is a good case that will support all these case front connectors ?
Connecting all headers is not required…
If "audio" means that the computer should be as quiet as possible, you can't go wrong with the Fractal Define family with a Noctua NH-D15S or NH-U14S cooler, and Noctua NF case fans if necessary.
But the possibilities are endless and we won't build the computer for you. It's your computer, your taste and your requirements.
