More motors more what?

I am planning to use 4 stepper motors of 1.5 volts and 140 N.cm (198 oz in) and 3.0 amps

Does more motors mean more any of these:
more amps
more volts
more watts
In terms of a 4 axis driver and a power supply.

Anyone know?

Voltage is the same, each motor pulls three amps, so more amps, more watts.

Since you'll be using chopper drivers the voltage is what you choose, its not a
property of the number of motors. It depends on the top speed you want.

Total power is sum of the powers to each motor and the losses in the drivers.

High performance bipolar steppers can pull a lot more power at high speed than when
stationary (not the case with unipolar steppers for instance).