I appreciate you doing market research before you begin, but on the assumption that you will be no more than a Facebook/Craigslist breeder in the immediate future (nothing wrong with that, officially, so am I), your market research is better tuned to your local area.
Still, on a very broad level, there are some signposts -
In general, there is no money in mutts (random mixed breeds/barnyard cross).
You can't compete on CX (Cornish Cross). You don't have the scale, you don't have the lines, you have no name recognition, you can't produce the quantity needed.
In general, dense urban areas with small flock limits (typically, 6 or fewer, no Roos) favor "vanity" flocks. Birds with unique feathering, birds with pretty and unusual egg coloring etc. Good money in those, but your males will be worthless - not only for sale, but likely on the table too - those really pretty, funny feathered birds don't tend to weigh much at an early cull date, while still tender.
In general, rural areas want eggs. The males might be worth something, but you could do a marginal business in sex linked hybrids - but you will likely be maintaining, effectively, three flocks - a great roo of one type, good hens of another type, and the hatchlings for sale. If there is value in males for meat, look towards some Black Sex Link variety, they tend to be a little larger. If there is no local value in males, look to red sex link - smaller birds, eat less, still prolific layers.
Finally, you need a way to set yourself apart from the Craigslist crowd. NPIP certification is the bare minimum. Look to your County Fairs, 4H, etc as a way to put your birds on display in the community you compete in, and also as a way to bring desired traits into your flock. Lose your best breeding Roo? Maybe you want to consider buying the winning 4H bird from the fall fair, if it has the right genetics for your sex link needs.
That's all I've got. No secrets really, just experience and practice. I'm doing, myself, exactly as I recommend above - though the lack of faires this past year has been "difficult".
and for what its worth, I have
a culling project going. The end goal is a dual purpose land race well suited to free ranging in my area. I'm not there yet. I don't expect to be there for several years, and until I get there, they won't be called "clay rangers", but that's the goal. **IF** we have a county fair this year, I plan to show a bird or two I don't mind culling - because its not re-entering my flock after that sort of exposure. I won't take that risk, its taken too long to get the few successes I can point to - and if I have no show worthy birds I don't mind culling??? Then I won't damage my fledgeling reputation by showing, and willl instead look to maybe buying. a goat.