Looking for Tips on building a fuel system

Recently my vintage Bracket car started leaking fuel from the pusher electric pump near the tank. I did not build the car myself and am changing things as they wear out and break. The pump and fuel system near the tank are not a pretty site. I originally just planned to replace the pump and keep going but I can't leave well enough alone. I still am running the Carter mechanical pump as well.

Money is an issue but don't want to sacrifice quality and safety for money.

How much fuel volume should I shoot for. Currently I estimate the motor to make approx 400 or so at the crank, maybe a little less. If I am putting new parts on i would like to upgrade the potential so if I am running a more powerful motor someday. I would like to be able to support approx 500 hp. Would you keep using the mechanical pump as well. What size fuel line. I may have the stock steel line in the vehicle still. 5/16 I believe.