High current in a parallel circuits
Your power supply must be able to suply the total currrent required by all loads.  You list three steppers at 1 amp, and a laser at 2 amps, and other things with unspecified currents, so you need a power supply that can provide more than 5 Amps.  How much more depends on the unspecified current requirements of the other devices.

If all devices are designed to operate from 12 volts, or are powered by suitable voltage regulators from 12 volts, each device will only draw the current it requires, as long as the supply can provide at least that current.