In most cases, it's best to see what others run in similar cars and choose what fits your needs. You can tweak others' ideas using the terms you listed so I'll try to explain them as best I can.

Watts: generally not important as it changes constantly due to varying voltages and impedance of the motors RPM changes.

kV: Number of RPMs of a motor per volt applied. A 4000 kV motor will turn 4000 RPMs @ 1 volt, 8000 RPM @ 2 volts, 12000 RPM @ 3volts, etc... Also, generally the lower the turns the more torque a motor will have.

C rating is dependent on the capacity of the battery(mAh). A 60c 1000 mAh battery will yield a 60a source, as will a 30c 2000 mAh battery. To determine the amp draw that a battery can sustain use the formula: (Cr*Cap)/1000; where [Cr] is the battery C rating and [Cap] is the capacity of the battery in mAh.

MAh is, as you correctly determined, the capacity of the battery and will give you an idea of how long a battery will run.

Finally, amperage (amps) is determined solely by the motor since it is the load in the circuit. Whatever the max current draw, measured in amps, of the motor will determine the ESC and battery you will need. In your give case of a 56a motor, a 60 amp ESC and a 20c 5000 mAh battery will be sufficient. When trying to choose an ESC for a motor ALWAYS GO WITH AN ESC THAT HAS A HIGHER AMP RATING THAT THE MOTOR!

Again, the most useful tool to use is the other members and what they run in their cars. If you still want to experiment or tweak their ideas, this info should point you in the right direction.