[njw]

the idea is that the master volume will be one which clicks at full. This means you can control volume and tone for each pickup (I prefer this to a blend pot) and the master volume means you can control both at once - for example, you like the sound of neck set at 70% and bridge at 100%... but you want to do a fade up from silence whilst playing live. Usually the only way to do this is to fade up one pickup, unless you have fancy hands that can operate two pots at once.

And yeah, the blue LEDs will be running from 1220 lithium cell will wont take up much room in the control cavity at all.