Lots of people suggesting to build chicken coop. i have one, sure it's not much work. 2 minutes every day to grab the egg and bring the food and water, but then every 3 year you got to take the hatchet, grab each chicken, cut right on the neck and then hang it with it's feet while it's bleeding out and flapping its wings. then there are the few occasion where you miss with the hatchet and it cuts half its neck, its h…
However, we do have a large yard where they are free to range around – I think this is key.
In my experience there is no need to kill a chook after 3 years. Average lifespan for a chick is 8-10 years. Egg laying frequency does decrease with age, but there's no need to kill them just because they're slowing down a bit. Our oldest chook is 8 years, and laid her (probably) last egg only a few months ago.
When it does come time to kill one for whatever reason, the broom stick method breaks the neck instantly - easy and clean, just a bit of flapping around. As for the body, we just bury them if we are not going to eat them.
I think the heirarchical behaviour depends somewhat on the breed and the environment. Our chooks do have a clear hierarchy, none of them have died as a result. We have a mix of breeds - Australorp, Plymouth Rock, ISA Brown and one other mystery breed.
Flies probably depend on your environment – in Australia here we have a ton of flies already, I don't think the chooks make much difference!
Some of our chooks have a lot of personality and are almost pets, especially the early ones we basically hand raised as chicks – although you don't want to be too sentimental about them either. You have to be OK with killing them if that becomes necessary - it's still a sad time when I have to do that though.
If you have enough yard space and like the idea of being connected to the creatures that supply some of your food, I'd totally recommend giving chooks a go.
* edit: should have added, we don't keep a rooster which probably changes the dynamics too