Another thing that occurs to me is that you might want different cap values (something darker...higher cap value) for the single coil than for the humbucker if you do go with the two tone controls. If you use a .22 with the humbucker, for example the same value may not get you much tone roll-off with the single coil. You might want something like a .47 The wiring diagram in your pic only uses one cap, but you can use a different cap for each tone control if you want to.