hi Tricky and welcome to the forum. We have another member, Bozza just setting out on his chicken-keeping journey, and on p.2 of another thread there are some replies about what sort of chickens to choose for a new flock, see http://poultrykeeperforum.com/viewtopic.php?f=124&t=11013&start=20
Four is a good number for your family - if you choose hybrids you'll be getting 3-4 eggs a day for the first year and nearly that in the second year. After that it'll drop off a bit but will still be worthwhile.
If you browse the Houses, Runs and Equipment section, there's lots of discussion about what sort of coop to get, and also what size and sort of run. If you're thinking of keeping four hens in the run attached to the Omlet cube, this would be good for protection against foxes at night, but not large enough for them to live in all the time. The Cube is expensive and has some disadvantages in my opinion, but there are alternatives. We recommend 2 sq. metres of run space per bird, for many reasons, so for 4 hens you need 8 sq. metres of run or a good -sized area for them to free range in. Chickens are incredibly messy, they poo a lot and will scratch up any grass they live on - don't be taken in by those Omlet photos of chickens on an immaculate lawn!
Good luck with your research, do let us know what you decide and feel welcome to add more questions as your thinking develops.