Well, do you already have a ESC and charger? What kind?
If you don't, get the Castle Creations MMM here:http://www.impaktrc.com/product_info...oducts_id=2524
For a charger, get something you won't have to upgrade later due to it not being powerful enough. I use a Hyperion Duo. It is no fuss charger that can charge 2 packs at once. Here:http://www.impaktrc.com/product_info...oducts_id=2386
Now for a battery you can choose 4S (4 cell), 5S or 6S. The higher the voltage/cell count, the more efficient it will be. This means cooler running and if your in a hot part of the country, this can be the difference between finishing a race and not.
For a good 5S, I would go with this pack to make 15 minute mains with ease. Here:http://www.impaktrc.com/product_info...oducts_id=3825
And now most importantly is the motor choice. It must be paired with the battery choice (ie: don't run a 4S motor on 6S). For a good match to the 5S pack, you could chose this:http://www.impaktrc.com/product_info...oducts_id=3844
With all these parts (a bit pricey), you will be set for racing in the brushless world for a long time. And you will be every bit as fast, even a bit faster than your nitro buddies.