a good alloy servo horn is a must, it will save you snapping the one you have first time the wheels need some turning.
as darkangel has said weight up the front twice as much as the rear, this will improve crawling no end!!
as for batteries, i wouldn`t bother putting the battery on the front axle (maybe just me), have a look at turnigy nano-tech 2s 1300mah, they weigh next to nothing and will give a decent run time, so buy 2 and enjoy.
looks like you got a great deal there mate, great rig/great electrics, couple of bits already mentioned and you will have a very capable crawler.