The Arduino is very good at detecting input, timing and turn on something.
The pedal board, http://line6.com/fm4/
The 'tap' detection needs some mathematical thinking programming. But you can always ask us for help.
Turning on leds is no problem.
Do you want to buy a foot switch or make one ?
A switch will bounce, so the code needs a debouncing function.
I wonder how that output resistance is connected.
Is one of the wires connected to ground ?
You can buy a digital programmable resistor, but the ground will be hard wired to the Arduino.