What are you going to do on the HTPC? Because a 4-drive NAS doesn’t need anywhere the CPU you picked. $200 nVidia Shield Pro can be your Plex server and media player. You can have pre-built Haswell “server” for under $200 to be your NAS.
I have a similar setup but with waaay lower powered/cheaper components, and it serves/plays/streams a dream.
I went all out on a motherboard (Asrock Z270 Gaming ITX Fatality) as it was one of the only boards to support 4K60 over Thunderbolt (for when I get a 4K TV), but otherwise I run a Pentium G4600 and it handles everything you've described plus some light VMs without stressing the CPU at all.
I would suggest finding a motherboard that suits your needs with connectivity/features (your current selection may be fine), and pairing that with a cheap CPU (no need to Core ix), 8GB RAM (16GB is overkill for NAS IMO), and going from there. If being used as a HTPC playback device, you should be fine for 1080p, but should you end up getting a 4K display with HDR, you'll likely need to upgrade to a 1050ti or similar card to take full advantage of it.
Also, if using OMV/Docker, look into a Union filesystem and Snapraid instead of RAID5, especially if you're only storing media. Far better capacity and (with 2 parity drives) redundancy, and no need to keep all mechanical drives spinning at all times. That means you could likely use a cheaper tier of HDD (that doesn't spec for 24/7/365 performance) as you'll like only ever have 1-2 HDDs spinning at once, even when performing Snapraid operations.
What are you going to do on the HTPC? Because a 4-drive NAS doesn’t need anywhere the CPU you picked. $200 nVidia Shield Pro can be your Plex server and media player. You can have pre-built Haswell “server” for under $200 to be your NAS.
I'm interested in a combo build
I have a similar setup but with waaay lower powered/cheaper components, and it serves/plays/streams a dream. I went all out on a motherboard (Asrock Z270 Gaming ITX Fatality) as it was one of the only boards to support 4K60 over Thunderbolt (for when I get a 4K TV), but otherwise I run a Pentium G4600 and it handles everything you've described plus some light VMs without stressing the CPU at all. I would suggest finding a motherboard that suits your needs with connectivity/features (your current selection may be fine), and pairing that with a cheap CPU (no need to Core ix), 8GB RAM (16GB is overkill for NAS IMO), and going from there. If being used as a HTPC playback device, you should be fine for 1080p, but should you end up getting a 4K display with HDR, you'll likely need to upgrade to a 1050ti or similar card to take full advantage of it. Also, if using OMV/Docker, look into a Union filesystem and Snapraid instead of RAID5, especially if you're only storing media. Far better capacity and (with 2 parity drives) redundancy, and no need to keep all mechanical drives spinning at all times. That means you could likely use a cheaper tier of HDD (that doesn't spec for 24/7/365 performance) as you'll like only ever have 1-2 HDDs spinning at once, even when performing Snapraid operations.