1.) Yes, with the battery in the front it will help you get over rocks and "Wheely" less.

2.) Not sure, I searched for a while but had no luck. Try your LHS too though.

3.) I am not sure how that is even possible. It can be done if you use the stock setup and somehow run some another linkage to the rear from the center pivot point. You would need a very strong servo though, and you would not be able to steer the rear tires independently.
Your best bet is to upgrade to a 3 channel radio, then you also have control over the rear wheels.