There is not much difference at all between the '07 and '08 models. They are virtually the same exact vehicles with only 4 listed minor differences. There is a thread around here that list these differences. Search around for it.
We talk about buying price all the time around here
v8 usually runs about $1500 more than v6 model for the sport and sr5 models. Not sure that I've seen a limited with a v6 ever. stickers around here (california) for v8 limited are usually around 42k-44k depending on extras.
i'm on the cusp for buying as well. i'm waiting/hoping for 0% financing on a 4runner since I can't afford all cash.
I would consider aftermarket nav systems. They are generally cheaper, easier to replace, and fairly cheap to get installed.
option packages will vary slightly from region to region in the USA. for instance, a Sport Edition may not include sunroof as standard in Maine, whereas out here in CA they all come with sunroofs.