I think I've cracked the self-sustaining flock problem, at least in so far as I've satisfied my goals (which includes providing some food daily and safe roosting and nest space for those who want to use it).
Review of 2025 reveals I spent 407.78 and earned 570.25 (and that despite having 4 broodies off laying for months each, and almost as many males to feed as females). So for 3 years now I've not only covered my costs, but have been recouping some of the capital outlay that I spent when I started.
The flock size hovers around the high 20s, as I let broodies raise small clutches and I give away some birds. Home bred birds have excellent hatch and survival rates; bought in hatching eggs not so, but new genetics are, I think, essential to keeping the flock strong and healthy.
I see new behaviours every year as the flock composition changes; I think it is getting closer to a natural state each year. Allowing them to choose their own mates, and not culling oldies or 'excess' males, both play significant roles in the change I think. Almost all traditional wisdom on poultry is based on observing the behaviour of birds born and raised in highly artificial, manufactured conditions, not least living in a flock full of youngsters with a very peculiar sex ratio (a phenomenon exacerbated by the closer to the present one looks). Isn't that more or less guaranteed to produce abnormal results?