The USB 3 cable will not be blocked. The picture of my 8700 is at an angle so it is hard to see.
The graphics card will take two slots. The one shown by #16, and the space below it where there is no slot on the motherboard.
The USB header is shown in box 7.
note: There is a second PCIe x16 slot on the bottom but that is not where the graphics card will mount.