If you dont want the protection of having no fule supplied to your motor unless it is running and has good oil pressure then you can run the wire from any wire that is on when your ignition is on.
Using a relay would be a good idea as would a filter. Some filters arnt really ment to be sucked through and can starve your motor. All you need is a filter to keep big chunks from getting sucked into the pump.
Most electric fule pumps prefer to push as apposed to suck fule. If they are sucking then they tend to die quicker. That means you should stick the pump as close to the tank as possible and preferably below it so gravity is basicly feeding it.
Also be aware what pressure its spitting out, it might overpower your needel/seat in the carb and piss it off. You might need a regulator. Different carbs like different pressure.
I prefer to run mechanical in most cases since they will provide plenty of fule to most motors and you dont have the head aches but its your rodeo. I would recomend having a spare since they tend to [censored] on you with no warning at the most inoportune time.