3-5x bb raise is right, maybe more if the blinds are small. The point of the raise is to get the true crap out of the pot, so someone doesn't flop 79 and get 2 pair. Limping or doing something else is appropriate at times, but it's a special situation thing. If you raise and get a reraiser then the best thing to do is put them AI with AA. With KK, if you think they have AA, I would fold and live to fight.