Arduino Wireless Combination Lock With NRF24L01 and 4 Digit 7 Segment Display

This project started its life as an exercise to do something with a 4 digit 7 segment display.
What I came up with was the ability to enter 4 digit a combination number, but once it was finished, it was quite boring. I built it using an Arduino UNO. It worked, but did nothing else.
I then had the idea that it should have a button to accept the selected number, and maybe another button to change the combination, and maybe an LED to show the state it was in at any time. Whilst it sounded like a plan, it also meant that I would run out of pins on the UNO. There may be a way of multiplexing this unit but I’m not sure where to start, so I reached for the Arduino Mega.
Now that I was using a bigger board and had more pins to play with, I also decided to add wi-fi capabilities to communicate with another Arduino which would actually control some kind of switch.”