Its 2 slots if you dont count either PCIe 3.0x16 slot. Else 3 if you count bottom/top slot , or 4 if everything including PCIe 3.0x16s is counted.
Dual GPU will be possible with a long adapter.
Its PCIe/PCI layout goes this way -
PCIe 2.0x1
PCIe 3.0x16
Empty Space
PCIe 2.0x1
PCIe 3.0x16
PCIe 2.0x1
PCIe 2.0x4
Each thing takes a slot. So yeah , you must have got it.
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