Hi, I have had chickens for a year this month, I recommend you read a lot before you buy, but saying that don't be afraid to take the leap and get your hens when you have a grasp on the needs of the animals.
The coop is important, it must be big enough for the amount of birds you have. I made my own by looking at google image for inspiration. Important factors are size, shelter, and ventilation. It might seem a contradiction that chickens need good ventilation but hate draught's if you get it wrong the chickens will not be happy. adjustable ventilation is a plus, and the angle you situate the coop away from the wind is equally important. Raised coops on stilts are good protection from rats, and the winter cold, and also makes use of space as my chickens love to shelter from the hot summer sun underneath. I lost one chicken to what I now think was heat stroke!
I added a plastic roof which I read lets in light and reducing red mite but I am not sure if this is true. I have a large heavy coop and run which does not move, some people prefer to move a smaller coop from area to area. This helps prevent a build up of nasties in the soil and you do not have to clean the run, just move it! always think...is this coop easy to clean? if it is not, do not buy it!!! you will soon find a cleaning routine to suit the coop and amount of birds you have. I give quick clean out of bedding and poo once a week, and a deeper clean every few months.
I suggest you attach a fox proof run to the coop for the reason that you can leave the coop door open during the night and the hens can let themselves out in the morning, giving them and you some freedom. otherwise they will wake you up and tell you off for not letting them out! when you get up you can let them out into the rest of the garden if you like. chickens also eat slugs, snails, bugs beetles and grass, but also plants and flowers. They enjoy digging up bulbs, they love bananas, unguarded sandwiches and have an appetite for destruction of neat gardens. Most people suggest you limit kitchen waste treats (but cabbage is good and helps keep them occupied and can be hung from a string) give them recommended feed and corn mix as a treat, you also slip them medication against internal parasites once a month. A fresh supply of water is vital.
the advice already given is sound. with more knowledge you can prevent problems later on but when things go wrong it is up to you observation skills to notice the signs and seek advice. check feet for scale problems, under the wings for lice, and their bums to make sure they are clean. above all keep them stress free, stressed birds get sick more often and sickness can spread. One last thought, think to yourself, if I have to isolate a sick hen, where can I do this. You may also want to isolate broody hens ( all they want to do is sit on the eggs all day, and this does not always go down well with the other hens)
Best of luck,