I'm in the suburbs, my city definitely allows chickens and my HOA is ambiguous. I have 4 standard hens, a 4x4 coop used exclusively as a bedroom and egglaying site, a run of about 20 X 20 and a fenced backyard. I initially only intended to freerange the girls in the yard when I was home, but now they're out all the time. They consider their generous sized run to be chicken jail, and one will consistently fly out. She has never attempted even the three foot section of my backyard fence, but the run is pure evil and she gets out everytime.
I consulted my neighbors before getting the chickens, and addressed their concerns about noise and odor. I share eggs to keep the neighbors sweet. In my area we have racoons, possems, hawks and stray cats. There are coyotes nearby. My biggest fear is stray dogs. Overall, so far I've found keeping four chickens is less work than having one large dog. I would like to enlarge my flock slightly, the city allows up to 10, but I don't want to tax my neighbors too much. If your neighbors work, they won't be home for most of the noisy hen time, and probably only those houses immediately next to you would hear them anyway.
I take lawn cliipings from one nieghbor and add them to my compost bin/chicken snack pile. This keeps the odor down. I use sand in the coop because it makes clean up easy, and I bury the poop in the compost. The girls mix the compost, grass and poo, yeilding crumbly brown odor free soil. I do have to keep scooping everything back into the bin, but that takes 5 minutes. I no longer put the lid on the compost bin because Shiner went in the side and couldn't get herself back out with the top on.
For me the biggest downside is poop on the patio.
Good luck with your urban chcikens.