Having worked this out for some other Organs, I was about to attend to this on the Salisbury. If I get any good results, I could post them later. Here is a general outline of my approach:
Using five divisional pistons for each division (physical pistons on my Console), Piston 1 for each division is something very soft... perhaps strings or celestes, perhaps Flutes 8' and 4'. Piston 2 is usually a full Flute Chorus, Piston 3 same plus soft Reeds. Piston 4 is usually Principals 8' and 4' and 2', Piston 5 a full Principal Chorus including Mixtures.
Then five General Pistons: Piston 1 uses Divisional Piston 1 from each division, and so forth.
Then five more Generals... same as above plus interesting Couplers for a fuller sound.
Then up to five more Generals... same as above but introducing the stronger Reeds, culminating in a big "Organo Pleno" sound with "everything" (excluding of course celestes and tremolos and any pipes too soft to make a meaningful contribution... and also generally excluding a couple of the very boldest stops which can always be added manually... such as the Tuba 8' and 4' on the Salisbury, and any 32' Pedal Reed (controlled by a separate Piston just for that).
Hoping this is helpful. -- OrganoPleno