A 780M is noticeably better than the Steam Deck GPU, which is what it’ll be compared to.
https://gpu.userbenchmark.com/Compare/AMD-Radeon-780M-vs-AMD-Custom-GPU-0405/m2088874vsm1804237
I suspect that price is a bit high for most people. I think it’s largely coming from those screens.
Yes. You insert the new disk, then just tell it to replace. It’s completely fine. I did this to upgrade the capacity of the drives in my NAS.