OK Dave; here's another micro manage, but I think I can save you another chip:
Idea #1 - save a chip:
1) make the rotary encoder a turn/push one, this saves a button (I know, but not IO at this point), and use the button to flip between modes: Voltage/Current, one other button for load on/off. By reducing to a single control; you save space, and already your front panel is pretty busy. Now you've gone from two rotary encoders and 5 buttons, to one rotary encoder/button + one stand alone button, saving front panel space and 6 IO pins
2) drive the RGB off the same lines used for MISO/MOSI/SCK. Who cares if your LCD flickers when you program the chip (3 more saved IO pins). (see radical idea below to remove Ethernet requirement from these pins)
Nine IO pins saved, No need to an IO expander
Radical Idea #2.
It's a cordless power supply, but has corded Ethernet? in the words of a famous EE from down under: "FAIL!"
Use an Electric Imp to provide wireless ethernet if you want it (i2C)