For batteries I would run whatever gets you around the track without dumping but be cautious about some of the "great" deals on some of the 4200's out there. They turned out to be a little more volitile than expected.
For your car most racers may overlook the idea that running what your LHS supports (parts wise) is a great way to go. If you need a part you can pick it up, and you would be helping to support the shop/track so you have a place to run.
It sounds like your well on your way though, so go fast and have fun!