Here's another way to do four pick-ups.
With 4 humbuckers = 8 single coils - perhaps easiest wiring would be a rotary 15-position pickup selector + Volume + Tone.
Top single - top humbucker - second single - second humbucker ( consisting of single coils 2+3 ) - third single - and so on.
Well - I correct my phrasing - not the easiest WIRING - but easiest button count with max combinations.
Or one could connect them to 10 different humbuckers + 8 singlecoils + HB/SC-switch + Vol + Tone
And after all this - how many REALLY different sounds could be achieved?
BC Rich in 80:s comes to mind . . . so many knobs - not so many sounds.