RAM will run at the highest speed the Mobo automatically handles no matter what the RAM is advertised for, that's where O/C comes in, but tbqh there's 0 reason to be pushing the DDR4 speeds you see now without running Hypervisors/LotsaHardcoreVMs. So, just get what the Mobo is rated for and use that, if the sticks can handle O/C to a higher speed then O/C it, only after determining a need for it. 32Gb is not overkill, 16Gb is quickly becoming a must-have standard for consumer rigs as everything is basically x64-bit now, though the 16Gb is mostly to keep your multitasking available (dozen+ tabs in a chromium browser, music player(s), Rainmeter, crypto software, Arma3, TS3, all at the same time can actually start pushing the 16Gb limit). Though, maybe kick it to 4x16Gb or 4x8Gb chips so you're using all the lanes for the memory instead of just half of each lane (matching colors for the memory slots are separate lanes).
The only reason you would need above GigE NICs is if your entire network within your home before hitting the WAN/ISP Modem (The Internet) is at a minimum full GigE AND you have apps/servers/services/storage that would require regular high bandwidth transfers. To get there you'd be running an actual server and using networking gear that could handle the load as it is. Also that Rivet NIC seems to be the integrated Wireless-LAN card.
For sound, if you're not a serious audiophile, the chipsets that come with the majority of mobos now are more than enough to handle your audio needs. A card can offload some of the processing for audio, give you 7.1, with specialized :stuffs: for eargasmic audio, but pretty unnecessary.
If you have the extra cash and your monitors are ALL the same, hell yeah get some stands they're dope, you might prefer a stand that you can angle the left and right monitors inwards, to give yourself more of a cockpit feel. Multimonitors for 4k @ 60 FPS, miiight be doable with the 1080s now, but 1080p@60 is definitely doable with mini-D and HDMI ports. 4k setups need enough mini-D ports on the card, plus the ability to push that setup (which even 1-2 years ago wasn't possible for multimonitor no matter the setup, but that's partly where the massive, curved, single monitor trend comes from). For software, you really don't need anything outside of what Windows comes with, I run DisplayFusion, but that's more for managing my backgrounds with Rainmeter.
Other than all that stuffs, build looks good. I'd personally like a SAN/NAS to hold all my media files, or at least a big arse mechanical drive to hold all the stuff you dont regularly access/need to run fast (And if you care about it, back it up!).
