You can connect the devices to a switch and access them both from your computer. You cannot raid the device to an EX2. You can connect a USB hard drive (such as a MyPassport) to the USB3.0 slots on the back to expand storage and backup files using the system backup feature (not a RAID configuration).
I don't believe you can. There are fixed options for RAID and I don't believe it would span between these units. Be aware also that I have had problem with this unit in the 16tb version. My drive keeps disappearing from my network. If I pull the power and let it restart it stays visible for a day or two then disappears again. Keep this in your mind when you purchase.