I am far from an expert, but maybe it's useful to hear from a neophyte chicken keeper too. So here are my answers from our experience with about 16 months of having chickens. We have an 8' x 3' coop and have kept between 2 and 3 hens at a time (no roosters!). Four would be a better number, but we haven't dived in that far yet. Apparently 3-4 makes a "flock". I do know that 2 is not the ideal number, because when one dies (and it will!) then there's a lonely chicken left. They are flock birds and like to have company.
What did they cost you, and how much do you spend to keep them squawking?
Our first two were given to us, but when we've had to replace chickens (the sad but undeniable truth of keeping chickens: you will most likely lose some to predators) they have cost between $12 and $15 per pullet (female chicken between 12 and 16 weeks of age).
A 50 lb. bag of chicken feed costs about $15; the same for the wood shavings or straw for the coop. One bag of food and one bale of straw or wood shavings lasts us about 3-4 months.
Those are our only regular expenses, though we did spend $16 on bird netting to create a safe space for them to be out of the coop and in the yard, but safe from hawks (after one killed one of our pullets. still sad!)
Do you raise them for the meat or for the eggs?
Eggs
Is it worth the trouble?
Depends. Do you like chickens? They are awfully cute. My daughter has one she's trained to sit in her lap. They'll follow you around making burbling noises. If you're talking about the cost benefit - are the eggs worth the trouble of the chickens? Not in our case - ours aren't laying anymore!
How much time do you spend per week cleaning up the poop and cleaning cages and coops?
Maybe half an hour a week to get the poop down to manageable levels, then a thorough cleaning once a month or so that takes a couple of hours.
Do they smell bad?
They do indeed. Though we have found that the Rhode Island Red breed is less stinky than the Buff Orpington we recently added. Perhaps because the Orp is TWICE the size of the RIR. She also drinks way more water, so her poop isn't as firm, which seems to make it stinkier. TMI, I'm sure!
Do roosters crow only in the morning like on the cartoons? Do I even need a rooster?
You do not need a rooster unless you want to raise chicks from eggs. Roosters can be aggressive and territorial, and they make a LOT of noise. And not only in the morning! Anytime they feel their space has been invaded or their hens are threatened!
Edited to Add: We live in a very high COL area, so chicken prices and feed/bedding prices might be high compared to other places. You can buy chicks cheap, but they require lots more equipment and they die a lot - a twofer we decided we did not want!