I have no real world exp with electric pumps but I used a parts house replacement mech "airtex brand same as yours" pump (class rules) on a circle track 360 2bbl 9:1 engine & had no starvation at 6400 at WOT at the end of the straights & that was with 5/16" line same as you. For a shutoff you could use one of the aftermarket oil psi senders with the 3 male terminals that would shut off the power to it when the oil psi drops to 15 psi (some have a different cutoff psi) and you would want a manual on/off switch to the relay so you can prime the carbs before you start the eng. You could wire it to the ign1 (run) circuit with a seperate momentary contact switch to prime the carb as needed. Not sure how efficient elec pumps are (compared to mechanical ones) but you might want to use a 3/8" pump/3/8" lines