Definitely use a relay or even 2 of them depending on how many amps your fuel pump draws. I would also wire in a bypass switch so you can prime the fuel pump when you want to with the motor off. You can hide it too for anti-theft deterrence. I have two of them so I can turn off the pump with the motor running also.

The trigger 12v power wire is the only wire that runs through switch and fuel pump relay. You run the "on" main 12v supply wire through your relay to the pump with larger gauge wire.

Use similar sized ground wire for the fuel pump. You can use the chassis as ground, but it is better to use quality, properly sized wire directly to you battery.

A quick search on Google will give you numerous wiring diagrams to choose from. I always use Marine grade switches, fusing and wire as the quality is much higher than most readily available automotive stuff. Make sure to use quality properly sized fusing or circuit breakers to protect your new wiring.