We were thinking about getting a second pallet jack to go with the gate. We have a standard wide blade and were thinking of getting a narrow short blade. That way we could have one on the ground and one in the truck and just load or unload straight in without having to worry about getting the jack and pallet onto the platform.
You want your lift gate platform to be at least big enough to handle a 48x48 pallet. You would then wheel the pallet out of the truck onto the lift gate (or off the ground onto the lift gate), remove the pallet jack and park it along side of the pallet for the trip up or down. Or simply wheel the pallet onto the liftgate and turn it so the jack and skid both fit. Two pallet jacks are not needed. Even restaurant supply delivery people who use pallet jacks and lift gates all day long carry only one pallet jack.
A bigger platform is better. Ours is 86" wide and 63" deep. That's big enough to put two pallets side by side while leaving the pallet jack under one of the pallets for the ride up or down. Bigger is better and safer. The more room you have to work on the platform, the easier it is to maneuver the pallet jack and freight. We've driven trucks with bigger platforms than what we have now and would not want to go smaller than 86x63.
Capacity of 2,500 lbs. is the minimum. Most of the skids or pieces of equipment we move around are 2,000 lbs. or less. But if you want to put two 2k skids or a heavy piece of equipment on the gate, you need capacity of 4,000 or greater. Ours is 4,500 and we have never needed more.