Anyone running an electric fuel pump should be using a safety cutoff switch like this one that operates on oil pressure. If the motor stalls out and you lose oil pressure, it also will cut off your fuel switch. You don't want to be stranded with a motor problem and have that fuel pump filling the boat with fuel through a faulty carb or broken line, etc.
http://www.cpperformance.com/products/Fuel_Systems/fuel-pump-safety-switch.htm
Talking with Bruce Martin a week ago, we had a discussion about installing an electric fuel pump in line between the mechanical fuel pump and the tank, to switch on and prime the carbs. When they're off you can still draw fuel through them to feed the motor (supposedly, depending on unit). Since Carters are notorious for needing a lot of prime, the electric fuel pump was thought to be a way to do this. I have no idea of what it would do to your mechanical pump, so I can't recommend doing this.
Paul