4k7's a safe value for LED Current limiting w/9v supply, the LED will light when 100k pot is in signal path, and go out when SP is going through Bypass jumper.
100k pot means when you're adjusting the pot, you'll get to lower volumes without increasing to as much resistance between the pot input and output [ground being the third connection].
Say a 100k lin. [for purposes of demonstration] is set to middle, so the signal goes through 50k, doesn't attenuate high frequencies as much as...
if the pot were 500k, set to middle, the SP would be going through 250k, enough to trim highs a bit more than lows.
However it appears you have a treble bleed cap to compensate for that effect [the .001]...you can mess with the values of the cap and the pot, larger pot values will need a larger bleed cap to preserve highs...If you notice it gets treblier when you turn the 100k down, you can reduce or eliminate the bleed cap.
As shown the switching/vol/indicator circuit will work.