Since you're using the switches to ground the circuit it will carry minimal amperage. Most of the amperage will be on the power side of the circuit. But that's why I installed a bypass switch in my Barracuda (see previous post), just in case my homemade NSS fail, I don't want to get stuck somewhere without being able to start the car.
I always carry a starter switch that I hook directly to the starter relay or a screwdriver in case the key start does not work. I also like to use it when I work on the engine instead of jumping into the car to start it.
But like I said if the switch does not work due to excess current, Then I will replace the switch and add a relay in the circuit to handle the power. The relays are just a few dollars each