Re switch. you could probably pretty much fit any stop switch, e.g. even one off a 2hp yamaha/mercury/mariner :
https://www.bhg-marine.co.uk/yamaha-...ton-3974-p.asp
Or maybe this:
https://www.ebay.co.uk/itm/374234898616
It's small, discrete, waterproof, only activates while you push it, so won't get knocked and accidentally turn the motor off where a toggle switch or "cap" type lanyard would (assume you have an actual kill cord on the remotes).
You'd need to check the wiring diagram on your motor to see if this could wire alongside your existing kill cord or find somewhere else, or maybe even you need a different switch (Normally open vs normally closed). Either way, hopefully this is a starter for 10..