ARDnew:
What is the best brand and price for the motor control board that you recommend? I have seen now some boards from 15$ to 80$! so am not sure!Other thing can't I make the Aurdino to control the stock automotive relays? I have checked the Bosch and Siemens style relays it seems the 5V from the Aurdino can't activate the relay coil and deliver power to the other pin relays, how I can do this? it seems there is no much information about doing this!!
Sorry, I have no information about high amperage motor drivers - I just know you will need them. It may be worth researching Electronic Speed Controllers (ESCs) for brushed DC motors as used for model aircraft and model cars. If they can handle the current they are very easy to control with an Arduino because they appear to it as servos.
Yes you can use an Arduino to control a regular 12v relay but the problem is that the Arduino can only produce about 20 milliamps at 5v on an I/O pin which isn't even enough to drive a very small 5v relay. That means you will need to rig up a transistor circuit to allow the Arduino to control the relay coil current through the transistor. It's not difficult - Google should be able to advise you.
...R