Yes, i think, GPU is PCI Express 2.0 x16, and motherboard has "seven PCI Express 2.0 x16 slots", anyway read other's ideas, or google a bit, because i am not an expert in it (you gave me idea, i will read about them)
no expert ,but what are you planning on using the computer for after its built .
you did notice the board uses a Intel Xeon CPU right ,which if im right would make it a good video editing and Cad type workstation ,not a gaming cpu .unless it has become one ?
i have a older xeon based computer and its a Dell Workstation ,not a gamer
from Wikipedia =The Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.