1) They are compatible with each other. I would check the QVL from either G.SKILL or ASUS to make sure they are certified to work. It gives you the best chance that there will be no issues. If not on the list by either companies, doesn't mean it won't work. It just means they are not certified to work.
2) I would go with DDR3 1600 memory if looking to overclock. It gives you more room to adjust your settings to help with a stable overclock. The DDR3 1333 will not necessary hold you back but for the little cost increase, I feel it is worth it IMO
3) The motherboard supports DDR3 1600, it just isn't shown on Newegg. When you see the memory going from 1066 to 2000, it supports the memory sizes inbetween.