Actually this mobo can do 8x/4x/4x with 3 cards installed and only with ivy-bridge CPU.
Getting 16x/16x in SLI is impossible (cpu can't handle that much pci-e lanes). However this is not something to be worried about. PCI-E 3.0 8x has more bandwidth available than GTX690 can saturate. So even with most powerful cards there won't be any performance drop.
To get 16x/16x you need a motherboard with additional PCI-E controller, like Asrock Z77 Extreme9.
4 memory modules put more strain on CPU (memory controller) what can cause instability on very high overclock. However, once more, it is not to be worried about unless you are planning on some serious OC. Other thing is that you don't need more than 8GB of RAM (at least for gaming) so best option is to go with two 4GB modules. Personally I would go with 8GB of either 1866 or 2133, CL9, 1.5V.