The 3570k appears to be in your price range, so it should be adequate for gaming. You can use any number of brands for the ram; I've used corsair, gskill, patriot, crucial, kingston and samsung. If you don't want to overclock, you can save some going with a b75 board and non K cpu; you should leave enough for a video card upgrade.
Depends on the price or package deal. The B75 boards are a good value if you don't need too many features or overclock; get one with four ram slots. The 2700K is priced pretty high still, unless you find one used from someone else who is switching to ivy bridge.