Ideally you'll want to be using PCIe extenders for all rigs with multiple cards, not many motherboards can cope with more than 4 without them.
These PCIe Extenders are flexible wires that plug in between the motherboard and graphics card to give extra room and allow you to use all the PCIe slots. It is worth getting powered extenders, as many high end graphics card tend to rely on the extra power usually gained from the motherboard.
Most GPU's you'd want to mine with are double or triple width (slot size) so they take up a lot of space, blocking nearby slots if you plug them directly.
This one you picked probably can't do more than 2 GPU's, slotted directly in the motherboard.

The speed (1x / 4x / 16x) means the transfer speed of data across the bus, but since the amount of data is tiny it can work on even 1x speed.
Also PCIe 2.0 or PCI 3.0 doesn't matter either within reason, as they are both compatible with each other and while their is a speed difference it won't effect a mining rig.
You only need to worry about it's speed if the GPU is going to be used for large data like gaming for example.

Good luck.