Add features to an Arduino sketch

I have a sparkfun 12 digit keypad ([login to view URL]) which i have connected to an arduino uno. The way it is connected is all contained in the sketch file attached. The code is mostly written but I need help with the following: 1) Sleep mode, the only inputs which are exposed to the user is the 12 digit keyad. After 60 seconds of inactivity the arduino should power down in the greatest power saving mode possible while still allowing a user to wake it up by pressing any button on the keypad. My research says I need to use interrupts but I do not understand them. 2) recommendation of battery, I would like this to run 6 months to 1 year without changing the battery. Based on the power level usage, about 1 operation per day, what type of battery and how should I connect it to the arduino. 3) Memory save of pin code, the pin code should be coded into the eeprom and read from there during a reboot. i have coded a function to change the pin code but it does not set it in eeprom, it will need to update the old pin code in eeprom 4) General code review, this is my FIRST arduino project, if you see a better way to do something that I am doing i would appricate the feedback in comments! thank you so much.