+1 what
@ChickenChick46 has to say about the FlockStar app. So much more convenient than spreadsheets or notepads, in my humble opinion. Just log expenses / eggs / etc. on the go and the charts are there ready for you.
Also +1 what
@DobieLover says about waiting for next year to add to your flock so that you are rotating in fresh producers. Note my perspective is that I have plenty of space to retire my old biddies. Others choose to cull at first or second molt for efficiency. You need to decide for yourself how to approach aging egg layers.
Good luck on your chicken journey!