I have ordered a set of 5 PCBs so that I can start developing the firmware. I was going to breadboard everything but it was becoming a tangle of unmanageable wires with only 4 digits, 6 more along with 16 LEDs would be a monster. PCBs are so cheap and will save me the headache of wondering if my wiring of the breadboard is wrong so there is no reason for this project not to jump straight to a PCB.

I am not happy with how large I had to make the board and want to try to stick to the cheaper 100mm square PCB size or less in a future version. 

I will have to abandon the 6mm tactile switches for the binary input to get the width down. If anyone has any suggestions for switches let me know. I was hoping to find illuminated ones but they are about the same size as the 6mm so no width savings. I may have to play around with not lining them up in a nice row, it bothers my love of straight lines but it may be necessary. 

I also will have to see if having transistors to drive the LEDs (at least on the sink side) are necessary. If not then it could save a lot of wiring and components! Otherwise I will look into transistor arrays (ULN2003A?) or other options.

I like the 7 segment displays I have chosen, the LTD-4608JR 10mm 2 digit 7-segment display from LiteOn, they are super bright with very little current. I don't see a reason why these will not be used in the final design.

Here is a render from KiCAD minus the components that I could not easily find 3D models for.