Seems like you're making things overly complicated to me.
1) Why are you running the LEDs at 24V? You could just run them at 5V and waste less power. You need roughly a 110 ohm resistor (assuming a ~1.7V LED drop) to get 30mA.
2) Since you have between 2 and 10 LEDs, you need 10 independent drive circuits.
3) This can be accomplished with a simple single MOSFET per LED. See circuit below. You would use a copy of this circuit for each LED. (NOTE: The MOSFET and LED part numbers shown are just the default - make sure you use a logic-level drive MOSFET).
4) Depending on how bright you need the LEDs to be, you can probably just run them directly from the arduino IO pins. Many little indicator LEDs will be easily visible at 1-2mA.
simulate this circuit – Schematic created using CircuitLab