Seems like a solid deal. Not sure why it doesnt natively support DDR3 1600. Almost all motherboards support up to 1600... but it is a budget/value board. In real life, you probly wont notice the difference anyway.
I couldnt find any specs on it as far as PCIexpress crossfire setup goes... but it definately will be x8x8 without a doubt.
*The x8x8 is based on 16x. Simply put... the motherboard only has one 16x bandwidth. So when you use two cards... they share it (8x each effectively)
This wont make a difference really if you want to crossfire two 5770's... you'll be fine. Only way it may matter is if you tried to crossfire two 5970's or something with huge throughput.
Seems like a hell of a deal for the price for your basic computer/entry level gaming needs. Go FOR IT!