I bought 4 chicks. A week later I bought 5 that were a week old. Now 7 monts later, I bought 10 and hatched 5. I have 27 eggs in the incubators. 10 of the chicks from this hatch are sold.
And I am adding 3 rabbits to my household on Monday.
8 should be a good start. Chicken math strikes people differently. Last year I wanted 8, changed my mind to 10 at the farm, ended up with a free 1 (bakers dozen special) so total of 13. Due to illness and unwanted cockerels, I was down to 10 earlier this month. Then a couple weeks ago I got 8 chicks. So... it does happen.
Best advice I can give is build a coop that will comfortably hold way more chickens than you plan on getting!
Oh! And one more piece of advice.. it's good to stagger your flock ages. Egg production will go down as they age and you'll have to factor in molting season. So get 8 this year and maybe 8 next year.