I would not worry about a throttle body for now. Personally I don't think they're going to do a whole lot, and for the price that they cost, its too much to hardly get any power. And if you were to get one, a 70mm is way to big unless you are pushing a lot of power. I'm pretty sure Edelbrock makes a 65mm TB which would be fine I would say. But I wouldn't go with the TB untill later.

Do what some of the others said. Buy a good header, get the Greddy exhaust, and then a straight cat and some good driving you will come pretty close to mid 15's I think. I would also look into getting that Skunk2 IM, it helped my gsr out a lot in the top end.