13 R3, SSD NVMe

Hi there,

I'm about to upgrade my Alienware 13 R3 with a new SSD, not for gaming purposes.
Is the second slot PCIe 3 so does it make sense to mount a NVMe 3000/2800 speed?
Is there any peculiar size for the Alienware 13 R3 SSD or I can go for anything on the market?
Is there any compatibility list around here to avoid known not working NVMe?

thanks