I can help you develop and program this omni directional robot.
I am currently in the process of building one for my self that uses a color sensor for line tracking ir sensors for tracking a mobile ir beacon that it is supposed to chase and capture. It is using an IMU to make more accurate movements. I have designed a custom arduino mega board that i am using to achieve this. It contains 8 ir sensors, a port for an adafruit color sensor, a port for and adafruit IMU. 6 brushlless motor controller ports. 4 brushed Dc motor controller ports, and 4 inter-phases to connect to lego mind storms based sensors and motors. I am willing to share these designs with you to help you develop your robot and help you program it.
I just have one question what kind of line to you need to follow and how do you plan to trace it, would it be using color, ir, or ultrasonic.