Well considering I have kept hens for a whole week I consider myself almost completely under-qualified to answer these questions... but I'm not one to keep my opinions to myself so here goes.
which chooks are the best layers?
Hybrids, like red said - we got 2 hybrid girls last week and we read on the website of the manufacturer (yes, I know, a an manufacturer for living creatures
) up to 300 eggs a year at peak production.
how old before they start laying?
around 17 - 20 weeks I have heard - I think my girls are 18.5 weeks and still not laying
where would i get rescued battery hens from and do they still lay?
BHWT as already mentioned, I think there used to be a website called 'henhouse' I might be wrong though - same idea.
They do still lay a lot and are often less than 2 years old, but they have passed their optimum lay age. I decided against ex-bats as they can be emotionally draining, I needed working, healthy birds that already knew how to be chickens and weren't going to die of stress within the first few weeks. Many ex-bats will never have seen grass before, or felt the sun on their backs
A truly noble thing it is to rehome ex-bats and we might do it when we have more chook experience.
i want to make my own hen house but not sure what it needs, can anyone advise please?
I made ours, and I am just about to go and clean it out. Simplicity is the key, they need a perch and a nest box and a wee bit of space to walk around. I made big drop down doors on the back of ours so it is easy to sweep out all the lovely poop. I also attached an old curtain wire to the pop-hole door so I can open and close it without having to go into the run or get my fingers pecked. It is most important that the house is rat and fox proof.... both of which will kill and/or eat your girls.
what time of year do the hens start and stop laying, also how old before they stop laying?
Some hybrids continue to lay right through their first winter and it depends what breed it is as to how old it is when it stops laying - general consensus is that a bird has a limited amount of eggs, those who lay through winters will stop laying younger.
Do you eat them when they have stopped laying or keep them cus they are just so dam cute?
Personally I don't find them cute - I think of them as farm animals, not pets. I don't want to keep them beyond laying age but I still don't know if I have what it takes to do the deed though... time will tell.
Is it true that corn fed chooks produce better eggs?
I agree with red here, a mixed diet seems best, with loads of greens available. We use layers pellets as the staple food and give them other bits and pieces when we are about.
My 2 year old feeds the chooks (we have them in a small run that we move around) and she talks to them "hello girls, want some food?" she doesn't like when they come up close to her, I think she fears the beaks which look pretty fierce to me too. They are fun to watch though, for kids and adults.
We haven't named our chooks, as we don't want to create a persona for an animal we may end up eating or picking up in a plastic bag when the fox gets her. E (the 2 year old) is quite happy with this and I am pretty sure that if it is delivered to kids as a matter of fact there shouldn't be a big problem.
or keep them cus they are just so dam cute?
and hopefully drive the message about evil Mr Kipling and the other culprits (whose exceedingly good cakes contain battery eggs! 
) at the same time 
- wot? No chickens?