General feedback...
I have a (Asus) z68 gen 3 rig running Win 10 x64 (SandyBridge 2600k CPU) with a GTX 660.
Card compatibility:
SandyBridge CPU = PCIe 2.0 Spec (you)
IvyBridge CPU = PCIe 3.0 Spec
Negligible performance difference between 2.0/3.0.
1. It was an upgrade to 10, no issues.
2. AHCI (for sure)
3. This will depend. Stick with F10. Only upgrade to U1E if absolutely necessary.
4. It will work, you may have to select Gen2 for GPU Option (not Auto)
5. Stay at F10
6. Can't speak to this sorry. I'm a gForce guy. Although I have owned several Sapphire and HiS Radeon cards... gForce drivers have
ALWAYS been less buggy and more stable in my experience. YMMV
Gigabyte's 1050Ti is a nice little card. Twin fan, it will be quiet, but be sure you have good front to rear airflow through your case. Not sure where you are... Newegg has it for $149 with a $20 rebate.