I am not sure about driving them directly there is an ideal continuous limit of 20ma per pin with a max surge of 40ma. Overall the Arduino can source a few ma (200) and sink a few more (400) but the overall max I would have though was below your required limit.That does also not take into account the stall current or the inrush. This is especially relevant if you consider that you are stalling the motors at the end of travel whilst you count up to 600 steps in order to calibrate them.
here is a good reference for you to follow Arduino Playground - ArduinoPinCurrentLimitations
counting the pulses is not a difficult job but reacting to rapid changes will depend on the frequency of sampling.
You would be better off having some sort of limit stop at the beginning of travel so that the Arduino knows where the start position of the stepper is. It can then step towards the stop switch and set its zero point.
Feel free to send me an email to Peter@embeddedAT.com if you want to chat about this some more.
Cheers Pete.