I can count down from 9999 to 0 no issues
From 9999 what? Seconds? Minutes? Phases of the moon?
I would like to have the ability to set the time with buttons
So, if you button one button that means what? If you button three buttons, what does that mean?
Using switches is so much easier.
display period length on the adafruit 7 seg display.
In minutes and seconds? In minutes? In seconds? In phases of the moon?
If you have time in seconds, converting that to minutes and seconds is trivial, using modulo (%) 60 and divide by 60. To put the two values into a single variable, multiply minutes by 100 and add seconds.