It’s drawn from the bottom. Emitter towards plus (see here).
The LED does not actually do anything to the sound itself, correct? It’s just a pretty light as far as the circuit is concerned if I understand correctly.
Well, it shows that the oscillator is oscillating. If the transistor doesn’t do anything, it won’t light up.
For the complete instrument that might not be intolerable, but it also might be better to have a buffer of some sort.
You can add a simple summing mixer, see e.g. here for a 6-input mixer that you can expand to any number of inputs (mute switches and potentiometers are optional, the 100k summing resistors are required).