The how-to part. This should work with any number of parts in serial, yes?
Yes
Depends on what you mean by "parts". For any series wired resistors it will. However if there are LEDs in the series string their voltage drop remains constant regardless of the actual forward current flowing through them.
It doesn't matter what is in series, there could be marshmallows (as long as they conduct electricity), if you determine the current through any of the resistors using Ohm's law for that resistor then you also know the current through the other parts, including the marshmallows.
Don