We (Coastguard Hat on) used to have a 2.5P 90 with a Capstan winch, we had two of those red plunger switches on the bumper which were together wired in series with the coil supply, so they killed the engine when pressed.
In terms of which switch, I'd want a mechanically latching switch so that when it was switched off, it stayed off. there's not much point having a switch that can be turned on as easily as it can be turned off.
you could either use a (rather bulky, but easy to see) plunger type
Or, you could use a 'kill-switch' as fitted to powerboats/RIBs etc, usually this requires the driver to wear a lanyard (red string in pic), which if pulled kills the engine. There'd probably be problems with mobility, etc, but the advantage of this method is you don't need to be able to reach the switch, just to yank the end of the lanyard.
The stop solenoid only needs a very minimal current, somewhere around an amp, at a (don't quote me) guess, it'd be very easy to measure with a multimeter.