Thanks for all the pointers.
Yes, I upgraded my GPU when I got my 4k monitor a few years ago, so it's not too out of date, but acknowledged that I may eventually want to upgrade.
There are an insane number of almost-identically-spec'ed Asus motherboards (I see 8 different ones on pcpartpicker with just the Z370 chipset and their comparison shows them all to be identical). Are there better ways to tell the difference?
And then what kind of cooling is recommended?