Great insight, thank you.
However, I guess I cannot use the MCP 4018 breakout as variable resistor since the input current on the wiper pin is restricted to 2.5 mA. I managed to manually dimmer the LED brightness via 10K potentiometer but that was just to comfort me 
I'll try to better dimension my entire system and then go for a PWM LED driver (such as the TI TPS92512) starting from a battery voltage of 24V.
I'll keep you updated.