As for the licking wherever part. The clitoris is the best spot, it's located at the top of the vagina under some skin. {i} It's the dot in the i there
Licking all around the vagina feels good for her, so do that for a while, but when you want to get her to cum, go to the clit and keep the rhythm steady. It's made of the same nerves as your penis, and reacts the same way, so think of it like what you want her to do to her. Good head involves a lot of licking all over the shaft and balls, but you're not going to come that way, you need for her to keep a steady rhythm on your dick. Same goes for her.
One finger is probably all you need, two is good, but from what I've been told there is little difference in sensation, I mean it's still really small compared to a dick. Your aim with your finger is to rub her g-spot, not fill her up. Her g spot is located on the top of her vagina, between 2 and 4 inches in usually. Usually she'll complain that it makes her feel like going to the bathroom for a minute or two, then it should feel great for her.
There is no such thing as a girl who can't cum from oral, only guys who are doing it wrong. At least, I've never met her.
Cheers and happy licking.