It was time to step up my breadboarding game so I made some improvements. A ZIF socket so I can remove the PIC16 easily. And plenty of space around it so I won't accidentally pull out a jumper.
The input-elements are on their own self-adhesive "island" and all peripherals are on their own detachable block. This block has the most common stuff ready to go and can be made powerless by the MCU when it goes to sleep.
I have a prominently marked, robust on-off switch because when I used a tiny pushbutton I couldn't see whether things were on or off when the system was asleep. And when I slightly rested my finger on it, it already interrupted power.
With the main board having all the standard components in place (5V power module, electrolytics, decoupling capacitors, resistor network to measure battery voltage, the rest of the board is free to put only those extra on that I need for a specific project.