You'll only be able to "indirect mine" as in mine altcoins and convert to Bitcoin.
A Ryzen is overkill for a dedicated mining PC but it would make sense if you have other uses.
I am not so sure. I put together an X370 rig just to see. With a Ryzen 7 you can mine Monero + your GPUs can mine away as well.
Two advantages: using new cards like the 1080 Ti, I see better performance, more like 3.5 Sol/W than 3.x <lower> on an 1150 board using the exact same GPUs. Nothing changed but the motherboard/CPU.
Also, there is a speed bump up that I notice when using the CPU to mine; that is, the GPU hash rates jumps up a little bit when mining Zcash.
And if you get the 65 watt Ryzen, when the motherboard is just idling (not mining) you'll see right away that the power draw is a bit less.
Biggest drawback to Ryzen is installing Windows 10. If you get an old OEM disk with Win10 64-bit build 1507, for example, constant errors and freezes. Ryzen does not become stable until Win10 build 1511 or higher. But good luck using "Windows Update Manager" to get there. I would say, get at least to 1511 or build 16xx, and then stop there and mine.