how big of fuel line do i need

You will hear a lot of different opinions on this but here is what I learned long ago from some veteran drag racers.

A little too big is not as much of a a problem as a little too small.

The fact that the car doesn't die out and is not "starved" for fuel does not mean it would not run better and faster with more fuel.

For a race or serious street/strip car, start big at the tank and reduce the size at each choke point-the pump, filter, and regulator, etc. This allows the quickest recovery of pressure after a drop. I have -10 AN from the tank (pickup with a ½" tube from Year One) to the filter and elec. pump in my trunk, -8 AN from them to the regulator, and -6AN from the regulator to the carb. My fuel pressure is steady as a rock no matter what I do.

Mount the regulator somewhere where body vibration can not lift the ball off the seat and flood the carb. A carb plate is best.

Up front, run the main line up to the firewall and turn back toward the engine to feed the regulator because you want the inertia of acceleration feeding the regulator not starving it.

When I bought my car it was race only and the fuel system was silly overkill. It had 2 ½" lines from the tank to 2 electric pumps, then 2 ½" lines Y'd down to a single 7/8" (yes, seven eighths!) from there to the regulator, and 3/8 from the regulator to the carb.