Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
M.2 is just a connector type. You can have an M.2 SATA SSD that gives no benefits over a 2.5" SSD aside from form factor. Instead, you'll want look at PCIe vs. SATA.
It's totally dependant on the drive you buy. The PCI-E interface is much faster, but if the drive's max speed is 200MB/s you're not going to see a difference. I recently went from a Samsung 840 PRO to a Samsung PM951 NVMe drive which is 4x as fast, the difference is noticeable, but the interface is not the single defining characteristic.