For better range and accuracy, upgrade the barrel to a tight bore and put a new hop rubber in it. Maybe even if a hop unit if the stock one is crap.
For higher rate of fire, switch to a high voltage battery or upgrade the motor to a high speed one. A high speed motor will probably need higher mAh batteries because it draws more power from them. Rate of fire isn't really important, so I'd start with rubber and barrel to get the range and accuracy.