B450 vs B550 AOROS
B450 vs B550 AOROS
I received a prebuilt from NZXT and it's genuine. Unfortunately, the motherboard lacks a second M.2 slot for installing your old hard drive. I think you should go with the B550 AORUS PRO AC model.
You're considering swapping the mainboard for a PCIe to M.2 solution. That's a smart upgrade!
It varies based on the card you receive. Likely not. I've tried one from Silverstone before and haven't noticed any noticeable drop in performance.