If it's not really about tuning or wiring. Then it belongs in here.
Can External Fuel Pumps "pull" fuel or do they need to be gravity fed ?
They can "pull" fuel. The Bosch in my Landcrusier (bolted to the right side chassis rail) does. When it was initially fitted I pressurised the tank with compressed air until fuel was flowing out the tank outlet and then fitted the hose to the pump.
What pump(s) are you considering? If you check their specifications, there should be mention of their lift rating - may be as vacuum head - and it should state alsostate if wet (with fuel already in the pump and pick-up piping) or dry*. it will also depend on their mounting height compared to the fuel level.
*Important note, fuel pump generally use the fuel to cool them and running dry can overheat and burn them out.