On the Intel side, the i5 8600k is a pretty poor deal money wise if you ask me… I think the i5 8400 or i7 8700 are both better value, especially as you include coolers, however the 8400 may not be a big enough step up over the 2600, its only like 25% faster. But on the AMD side, the Ryzen 1700 OP suggested has better performance than the coffee lake i5’s when all threads are usable (and similar to the non-k i7 8700) and comes with the excellent RGB wraith cooler, so for non-single threaded performance bound tasks it really is better value, even if you end up with with a $20 display adapter. Although honestly getting something like the gt1030 so you have hardware h265 encoding and de-coding may be worth it to me for a media center PC, as the iGPU on intel doesn’t do that. Finally availability of the K series coffee lakes is very limited, while the non-k can still be found around.
Not to mention the fact that none of the new Intel hardware is in stock.
I know a lot of people get caught up on power consumption for these types of rigs. If a rig is built from scratch, with the proper funding, it is a valid concern. However, if repurposed hardware is going to be used, power consumption takes a back seat, as it should; it will take many years to recover the cost of new hardware through power savings.
My first FreeNAS rig was a repurposed LGA 775 Q9550 that used to be my main system; it served me well, even with the GT210 I needed to POST the system.
For a machine running several VMs, a build like my old rig is not going to cut it. A Ryzen system is a logical choice here, at least to me. A low power GPU will work perfectly for this application. The additional power usage would be negligable.
@SheepInACart it is nice to know that there are boards out there that support headless operation even with no GPU. This makes a system like the one proposed much more viable, with consumer grade hardware. I really appreciate the info!
I don’t really see the benefit from an Coffee Lake cpu, for me i would be paying bucks for a CPU mostly made for gaming? 
Anyway, think i’ve decided to build in full ATX instead, and then use a low-powered GPU to get past post