Buying chickens now shouldn't be a problem, I'm not sure if you can buy from a market but I don't see any reason for not buying directly from a good breeder which would be my preferred option anyway. Or you could look at rehoming some ex-battery hens.
You will need a run where you can fence them away from your garden. I tried to let mine free range in the garden and they gradually wrecked it. Now they're confined in a large run (about 5m x 5m for 6 hens, you don't need that much space though) and are only allowed out when I'm there to supervise them. If you have foxes visiting you will need a fox proof run, but you definitely need a fox proof henhouse so they are safe at night. One of our hens didn't go into the henhouse on christmas night, it was dark when I locked up and didn't notice, foxy had a nice chicken meal that night
We haven't experienced a fox problem during the daytime yet, thankfully as our chicken run isn't fox proof. There are lots of chicken houses and runs on the market, we use a childs small playhouse from Focus and a picket fence around it to make the run. As long as you can close it up at night, it has some ventilation holes and you can add perches then it will be fine.
At first I clipped their wings, but I don't do it anymore, they know where home is and have never tried to fly away. Clipping their wings didn't seem to stop them from jumping over the fence of their run so we had to make it higher.
Keeping hens in a residential area should be no problem at all. Make sure any food is kept secure so that rats don't become a problem, and make sure you don't leave too much food left scattered around on the ground. I've never seen rats where our chickens are, I'm sure there's the odd one like there would be in most places where the compost bins are kept. I keep my compost bins in the hen run, when the compost needs turning I empty the bins, let the hens scratch about in it for a couple of days before putting it all back into the bin again. If you're in a residential area you don't want a cockerel, they are noisy! Hens will happily lay without the need for a cockerel and you can hatch eggs without a cockerel, you would buy fertilised eggs (ebay sell them as do lots of breeders), but you need to plan ahead what you'll do with unwanted cockerels that hatch, we fattened them up and ate them!
The biggest expense is getting the hen house and run set up and buying the hens. After that they eat layers mash and crushed corn, a bag lasts a long time, and a little bit of straw or wood shavings for the nest boxes. They eat a lot of the scraps from the kitchen and reward us with lovely eggs virtually all year. As we have 6 hens we have excess eggs that I sell and the money goes into their food bill so effetively we get to keep hens and get our own supply of eggs for free. I lightly clean out the henhouse about every fortnight to once a month, that's a matter or taking out the wood shavings and putting in fresh ones. Once a year they have a good scrub out with disinfectant. I worm my hens every 6 month or so using Diatom, not very expensive and no need to withdraw eggs when using Diatom.
Kitchen Garden magazine usually have an article every month about keeping chickens.
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