1) Most likely a problem with your linkage settings at neutral. When you pull back on the brake you are closing the throttle opening as well. You need to make sure the collars and springs are adjusted so the card cannot close any more beyond your setting when the servo is at neutral. Also possible is a clutch that is dragging very badly at neutral (i.e the car won't stand still when the brake is just disengaged). Also possible is your idle setting is too low.
2) Check that the front diff will turn normally if you rotate the wheel by hand. If so, the diff itself and driveshaft won't be faulty, and it will be a problem with a binding bearing or wheel. If the diff won't turn, it could be diff damage or a damaged driveshaft.
3) Too hot for long engine life.
4) Fun don't come cheap!