z170a mobo is not needed since you can't oc your 6500
970 should perform a little better than a 470.
http://www.guru3d.com/news-story/radeon-rx-470-benchmarks.html
1. Get a different SSD that one I've never heard of. SanDisk, Samsung, Crucial for example
2. Get a different psu. https://geizhals.at/corsair-rmx-series-rm550x-550w-atx-2-4-cp-9020090-eu-a1331023.html?hloc=at
3. I am sure you do not need to list thermal paste there
Usable (from Merriam Webster dict): in good enough condition to be used.
It's not how much been used but it is how much available. For what I am seeing your computer still consumes same amount of memory after/before upgrade
There are no benchmarks so can't say for sure whether Kaby Lake will get a great increase in performance. For gaming Skylake is a good choice and should handle all the same smoothly. You don't need a 6 core broadwell for gaming at all