First off, good luck lol! Chicken math is real! It becomes an addiction after a while.

I started as a small flock owner years ago, today I am proudly part of the OCD community. Obsessive Chicken Disorder.
Just double checking, you know they can live much longer than 1-2 years right? Healthy chickens with a good setup, good biosecurity, and an educated owner, can have chickens up to 13 years old. Chickens can live a long time if cared for properly.
Also, for anyone building a coop, you should know these requirements. Note these are basic requirements, and I highly recommend you make the coop and run larger than necessary. Doubling the amount of space even. Then if you ever get more you will have plenty of space.
These requirements are per bird-
4sq. ft in the coop
10sq. ft in the run
1ft of roost space
AT LEAST more is better 1sq. ft of ventilation per bird.
1/4 nest box per bird.