Since it's M.2 SATA, something like this WD Blue will get you going.
Sure thing!
2TB M.2 - https://www.amazon.com/dp/B073SBW3VD
1TB 2.5" - https://www.amazon.com/dp/B09ZYQ84CM
Yeah, I'm not a professional photographer so these speeds are just fine for my daily needs.
Sure you can:
https://www.amazon.com/Blue-NAND-500GB-SSD-WDS500G2B0B/dp/B073SBW3VD
https://www.amazon.com/Samsung-860-SATA-Internal-MZ-N6E1T0BW/dp/B07822Z77M
Are you sure none of your Skylake motherboard M.2 ports support NVME? I guess it's possible if it's a less expensive motherboard but it's certainly not a Skylake limitation, my old Skylake PC on a Z170 chipset motherboard has a 950 Pro NVME system drive