Arduino automation - pause and cancel buttons

I am automating a sandblasting operation and have the following Arduino setup:
LCD screen, relay module (for turning on/off project-related machines), the Arduino, and a [0-9, A-D, #, *] (basically a 4x4) keypad.

The user will most of the time use the [A-D] keys to access preprogrammed durations, but it would be nice to also be able to input a custom duration using the keypad.
I'm almost done, except I can't figure out by myself how to program a button to pause the operation as well as a reset button that will bring everything back to the initial state, ready for another operation.

In summary, what is to be done is programming the following:
- pause button (pausing the timer, and deactivating the relays);
- cancel button (deactivating the relays and bringing the program back to initial state);
- "interface" for the user to be able to input a custom duration and a start button.

I'll upload my .ino code file so you can see what is going on.