Alan , Just got home, This working for a living screws up my free time
1) the relay is usually located close to the power source and the load as Dennis mentioned. The relay could be hidden be behind the grille off to a side out of view if you wanted.
Keeping the relay close to the load keeps the voltage drop to a minimum with the heavier wires doing the work and then the smaller gauge coil wires running back to the cab to turn things on and off.
2) I think you have the right idea with the plan , I am not sure what you mean by spot 1 and spot 2, Would that be the terminal location from the terminal block(panel connection block)?? I cannot quite make out the terminal numbers on page 1
But with a single fan you would only need the one output from the N.O. relay contacts to the fan motor.
3) use a good grounding method, I like to extend all the ground wires to a common area and ground them together and then to the frame or back to the battery or block.
I have found on old cars and especially trailer lights, most electrical problems are really grounding problems,
Now, looking into the future,, Are you planning to run the high and low beam relays for your headlights??? maybe they all can be hid in a shiny junction box or concealed in the same location behind the grille or headlight bucket area???,