We've got half a dozen hens and they're really quite hassle free. You need to accept that they will basically decimate any ground that you let them loose on - we used to let ours roam the whole bottom garden and after a couple of months there wasn't a blade of grass down there, we have since penned them into a smaller area (with an electric fence for fox proofing) to allow the grass to regrow (which it is doing with vigour due to the fertilizer-effect of the poo). They to a fantastic job of scarifying the lawn and removing things like dandelions, but same as if you spend all day going over your lawn with a scarifier you wouldn't have much lawn left if you did it all day, so I would recommend you have a confined, secure area that they spend most time in, and let them out for a couple of hours if you want them to give the rest of the garden a good going over - they LOVE slugs, which is great if you're growing veg, but the also like veg seedings/plants so it's a bit of a double edged sword.
Red-mite is usually only a problem associated with any house that uses roofing felt for the roof. A completely wooden or plastic house or one with an Onduline roof does not have this problem. We have a completely wooden house and have never had a problem with red-mite.
They basically only need food and water. We use layers pellets most of the time and usually chuck a few handfuls of corn out in the morning and evening. When it's cold, they get hot layers mash in the evening which keeps them warm and happy through even the coldest nights (like this winter when it was minus 10 degrees). You can feed them just scraps and kitchen waste, they will basically eat anything edible, but the quality and number of eggs they produce will be proportional to the quality (and quantity) of food they have access to. Our current 6 are laying 5 or 6 eggs a day, which is pretty good, but they are only about a year old and I expect this to drop off when they go into moult. When they moult, the lose some feathers, sometimes it's loads, sometimes it's only a few - when they do this, they basically stop laying as they keep their energy and nutrient stores for making new feathers, rather than making eggs. This is why farmed or battery chickens that you can buy look so ropey, it's not because they've necessarily been maltreated, it's that once they go into moult and stop laying the farm wants rid of them as they're not producing, only consuming.
You'll need a supply of straw (NOT hay, due to dust) for the nest-box area and wood shavings for the rest of the coop. They'll need mucking out about once a week, I mix the shavings, straw and poo into my compost heap.
That's about it. If you're on the iDave diet, the supply of eggs is a godsend!