Nice. I have the 1070 mini. Which method are you going to use to mount the power plug? I went the Dremel way so I didn't have to cut into my precious S4 Mini (which I ended up doing to accommodate something else, anyways).
I don't know how much RAM you have (which will only make a small difference going two sticks over one), but with one stick of RAM, the OC on your 7700K, both SSDs, your cooler and the Zotac 1080 Mini with its default OC profile, you're looking at a 270W load, which puts you into that 90% range. Not a big deal if you're not gonna be running this 24/7 or drop the OC on the 7700K if you get the 1080. Just thought I'd make you aware in case you weren't.
HDPLEX 300W will most likely handle it with ease, I just personally like to stay in the 50-60% range even on load because I'm looking for longevity in mine. Everybody is looking for different things, though. If you're looking for "bleeding edge" in ~4L, you go ahead and rock that 1080 like nobody's business.