Chicken keeper with 25 years experience. A few comments:
There are no advantages to keeping chickens yourself if they are in confinement and fed only commercial food – the eggs will taste just like commercial eggs. If you want deep orange yolks and real farm taste, you need to feed them table scraps, fruit, vegetables, bugs of all kinds, etc. Let them run about in the sunshine and scratch.
Shell hardness is a function of the amount of calcium the chicken has access to. Free choice oyster shell is the standard. Occasionally you’ll get a hen whose shells are weak no matter what.
Chicken poop smell is due to confinement. Let them run around, and deep-bed the coop (add a layer of bedding on top of the poop regularly, so you are making a compost pile, essentially).
By far the biggest reason people give up on home chickens is predation. Chickens are absolutely helpless at night (they go kind of comatose), and are dang easy to catch during the day. A system which will keep your hens safe from (skunks raccoons dogs hawks bobcats foxes owls weasels etc) should be planned and built before you ever bring a chick home. Raccoons have small grabby hands that can get through any wire netting save aviary netting and half inch hardware cloth. Many predators dig very well. I poured a concrete pad for my chicken house long ago and never regretted it. Chickens MUST be safely confined at night, when most predation occurs. If you think there is maybe a little chance a determined predator can get at them, you have not built strongly enough.
The other big challenge with chickens is that they attract rodents. Or rather, their feed does. Keep your feed stored in metal, and don’t leave feed out at night.
Chickens can ruin a planted veg garden in minutes. Only let them roam where you have nothing planted that can’t tolerate vigorous scratching by large clawed feet.
Breeds: since what I prefer are a lot of large eggs and a calm friendly temperament, I stick to the few breeds that have these traits – Black Australorps, Speckled Sussex. Other, more common breeds with these traits are Barred Plymouth Rocks and Rhode Island Reds (although I don’t really like the temperament on the last, they can be too pushy and aggressive). Sexlinks are a great choice for almost anyone who doesn’t want to breed their own replacement hens. These are first-generation crosses of two breeds with certain complementary color genetics, such that the male and female chicks are different colors. This makes chick sexing a breeze (in pure breeds, even a skilled sexer will make a few mistakes). They also partake of hybrid vigor. Some of my best layers have been sexlinks.
Even if I could keep no other livestock I would have chickens. Not only that they turn kitchen waste into wonderful eggs and useful manure, but they are personable creatures which make surprisingly good pets, one of the better pets for children in my view, being cheap to buy and keep, quite sturdy and easily tamed and trained.
I would never recommend buying “rescue” hens unless you intend them for soup, which is probably all they are good for. The cheap and fun way to buy chickens is feedstore chicks in spring, they’re only a couple bucks or so. They will have to have a heat lamp until they grow feathers. They will lay some that fall and then start in earnest the following spring. Point-of-lay pullets or 1st year layers will cost about $20. Don’t bother with any other age of chicken, it’s a waste of time, space, and money.
Chickens lay best the first year of lay, good the second, sort of okay the third, and thereafter usually poorly. Most people who don’t want to end up running a chicken retirement home cull after one or else two years. I don’t butcher my hens for soup, I just put them on freecycle or free craigslist and off they go.
If you are a novice, get a chicken book. I recommend Rick and Gail Luttmann’s Chickens In Your Backyard, but the Storey series books are also good.