4.6W means using a moderately large heatsink or a smaller heatsink plus a fan (chipset cooling fans designed for computers are very handy for cooling I find - small and quiet.
So what about PWM and speed control? You probably want this in order to ramp up the motor to speed smoothly (a 750W motor suddenly connected to its full supply will give a hell of a kick, its not recommended - apart from anything you can chip any gears).
Yeah I'll try and use PWN. I found this article great (it talks about controlling high current with a MOSFET). http://bildr.org/2012/03/rfp30n06le-arduino/
The stall current will be whatever the supply can give, I suspect the motor can pull 100's of amps at stall if allowed. That will explode your MOSFET so make sure the supply current is limited to 30 or 40A and ramp up the drive to avoid these startup surges.
Oh ok thanks, what's the easiest way to limit the current?
With those reasonable high voltages and currents you almost certainly need to drive the MOSFET gate with a MOSFET driver chip (otherwise drain-gate capacitance could cause the gate voltage to go out of limits and blow up the Arduino. In fact that MOSFET isn't logic level so you'll need a 10..12V supply and driver circuit anyway. I've used the DIP version of the MIC4422 driver before - its very rugged. Connect the Arduino pin to the input of the driver with a 4k7 resistor and you'll save the Arduino from damage should something go wrong with the high-power devices (this is a real risk with prototyping high-power circuits).
Oh really? So I can't connect and control the MOSFET directly from my arduino? Or is the MOSFET driver chip just extra protection for the arduino?