It's all difficult, as one has to have the fortitude to cull when necessary, without letting sentimentality to get in the way. You can do this in a small flock as well, as the addition of chicks will have to come, be they from the hatchery or from your own flock eventually if you intend to have eggs. At that point, the yearly or, as necessary, culling is even more important.
It also helps when integrating new chicks to have already thinned out the older flock....less older hens, less problems with integration. It's even more helpful if you let your flock broodies raise up some foster chicks so that the integration is done as a natural process by their own foster mom.
...and this is where the difficult part begins. Favorite hens. Nursing "back to health". "Lucky for me, I don't have to cull any birds". And, finally, "died from an illness". All these statements are why it's difficult to stick to this kind of flock management or to even start it....one has to realize that culling will happen, be it by predator or illness, so it might as well be you and it might as well be done while the birds are in good health so the meat is not wasted and, finally, it might as well be done for a good purpose.
That good purpose is to build a stronger flock so that when you introduce more birds into it...and you will have to eventually if you are not hatching your own....that you don't have the worry about what those new birds are bringing to the coop.
The relative size of the flock does not preclude the need for culling as culling will come whether you want it or not. It might as well be a good cull, done with purpose and giving the bird a more humane death than suffering with an illness.