Steering knuckles, diff covers and axle extensions are all good ways to get yor center of gravity lowered. Wheel weights or aluminum wheels are the easiest way to achieve this, but do add a lttle more stress on the motor and servo. I have not personally had any issues but some have.
I'll second the batteries @Jamr suggested, I picked up a few of those. I needed a replacement when one of my original batteries died and those worked well.
Welcome aboard, the most capable out of the box in my opinion is the Axial SCX24 Deadbolt. It is also the lowest priced SCX24. Almost anything you can imagine is available in the upgrades department for the SCX24 lineup. There are lots of good rigs but this would be my first choice....wait I...