Need help with Proportional valve control

Hello,

Is there anyone who can help me,
I want to create a new application using an Arduino and a Atos Valve Controller.
I have two external signals and a selector switch / potentiometer to control the Arduino:
A GPS signal, 130 pulse per mtr for measuring the speed (1-3km/hour XD)
A inductive (ABS) sensor for measuring the saft speed
And a potentiometer to select a preferred value
The intention is to depend on the driving speed and a preferred value, regulate the speed of a hydraulic driving axle.

n the past I have make a nice steppermotor activated device that react on the 0-5v signals from Lambda, trottle position and vacuum but I don't no to begin with the pulse signals from the GPS and inductive sensor.
Many thanks in advantage,
Rien