1) No I upgraded to the 10 Insider Preview months ago.
2) Yes, there's been no issues with XIV.
3) DX11 has worked flawlessly.
4) None particularly.
5) It's overall a smoother cleaner experience, boots up extremely fast compared to fresh installations of 8 and 7. Has plenty of power options and user friendly management. It can take a slight adjustment if you're one of those strange ones that avoided 8 and are coming right from 7, but it's not as jarring as 8 would have been that likely kept you away.

6) Nah, I've been getting massive OS upgrades for months due to having the insider access. I was basically a beta tester the entire time. I couldn't be bothered since it was just another slight update I had to restart for yesterday.