I am sure you can't put too many upgrade cards per motherboard either, which means you will need another $350 board to add more after a few modules upgrades, speaking of which... how many upgrade modules can your main board hold before I would have to buy another board to get more cards?
If you read the full description you'll see that one motherboard does not limit you to a certain number of devices. They run on a bus, which is extensible indefinitely, at least in theory. The bus can be connected with stacked headers, or via a jumper cable, so there's no capacity limit physically either. There will be a firmware imposed limit to ensure performance. Since the firmware will be open source, you'll be welcome to remove said limit.
Perhaps, if there's a lot of demand for multiple-miner boards, I'll adapt the design. Until that time, as it's been made abundantly clear, I need to prove myself, and to do so I think a good place to start is affordable, easily extensible, single core miners.
Additionally, I'd like to know where these bulk FPGA discounts are from, I've yet to find a distributor who will give more than a pittance of a discount on large orders.
Exact control and mining hardware specifications are listed in the newly updated first post. Specifics can be found there, but the control device will be a Microchip PIC32 and the FPGA will be a Xilinx Spartan-6 XC6SLX150 running at 200 MH/s with the current firmware.