If I were to add a second capacitor to this circuit of roughly the same capacitance (120uf). Would this circuit charge both up completely, and would the LED still accurately depict if the combined two capacitors are charged. Does adding another capacitor not work or cause the circuit to not work?
A second identical capacitor in parallel with the first would double the energy available to the flash, resulting in brighter flashes, longer charge-up time and fewer flashes before the tube fails.
It's not an LED it's a neon, but yeah it responds to the voltage in the capacitors, so it will still indicate that the circuit is ready to fire.