I would use ultrasonic sensor only to anticipate collision with a wall or a game object and slowdown preemptively.
Analog sensors like Ultrasonic rangefinder, Line Follower, and Gyro are subject to environmental noise (1) (2) (3).
The most important improvement would be to use some sort of sensor fusion algorithm like Kalman filter. V5 has plenty of memory and processing power for such algorithms.
I would use 2 tracking wheels mounted at 45 deg angle and augment it with a line follower for position re-calibration when robot drives over a white line.
This way, with just two tracking wheels, all forward/backward, left/right, and rotation around the robot center is observable (the only unobservable movement would be rotation around point where lines continuing along tracking wheels would intersect).
Also, you can Connect multiple sensors to a single port to overcome the limit of 8 legacy ports