How many FPGA can be attached to one computer? I am looking at this. Dual FPGA X6500 Mining Card Rev 3 (Without Heatsinks)

So we connect the card via USB and the card will mine?

Should I buy one FPGA or several ones? Where do I attach the FPGA? PCI? USB?
From what I know, you can connect basically any amount of FPGA cards to one computer through USB hubs. Case in point: