1. Did you upgrade after the release of Windows 10? (Jul 29th)
Yes

2. Did the game start with zero issues?
Yup! Thought did have to do another restart of my PC after the first full-boot. So if you're having issues here ... "Did you turn it off and on again? D: "

3. Running DX11 version of the game just fine?
Smooth as heck

4. Noticeable changes? (Game wise)
Honestly, it's just running a lot smoother.

5. Personal experience you would like to share about it? (Windows 10 / FFXIV with W10)
Not going to lie, it does take a bit of configuration on your side to turn off things like apps you won't use, Wifi-Sense, etc.
For those NOT using the enterprise version, there is a way to turn off data collection~ :3 Clicku!

Edit: 6. Did you follow up with a clean install after the upgrade?
Nope, I just went from 8.1 to win10 upgrade.