It aint quite as simple as it may seem.
1
Switch are rated in terms of volts by the insulation quality, and creepage and clearance distances inside the switch.
ie. the ability
not to short out (flashover) when said voltage is applied.
The "amps" is the rated current carrying capabilty of the switch contacts.
This is also dependent on whether the switch is to be operated with the load applied, or operated before the load is applied.
The contacts will break down (burn) faster if they make contact with load applied.
2
The amount of current required from the battery will depend on how much work the motors are doing.
Free running with no prop in the water, or small prop and small hull - realatively little current will be drawn.
Large prop pushing a lage hull, will require a lot more current.
The more the motor is loaded the more current required.
Increasing the applied voltage for the same power requirement will reduce the current.
Hope this helps.
John