As you know - fit one filter between the pump and engine, where you want that filter exactly is up to you.
If you want to be extra nice to your pump (give it a better chance of a long life), fit another filter between the tank and the pump - but this is overkill and not necessary.
I do have a second filter fitted.
I don't know the specs of your sub wire, but fuel pumps are a reasonably heavy amp draw. I used both wires of a twin core lead (each 3mm wire joined at each end) to drive the pump.
Ideally you should run a new 8mm fuel line as your engine will need a bigger fuel flow.
If you have to use the existing fuel supply line trace it back from the old fuel filter in the engine bay, or forward from the
pick-up in the tank.
May be best to pull out the tank to confirm the pick-up line, however in my car it is the pipe closest to the rear bumper, which makes sense as that is the way fuel flows in the tank under acceleration.
Mitch.