It sounds like you are on the right track with the things you are doing. The reason it's good to be feeding her kitten food is because the kittens are taking a toll on her body and kitten food is more densely packed with energy than adult cat food. So she gets more energy without having to stuff her belly with food.

I also think it's a good idea to confine her towards the end of her pregnancy, as some cats will tend to try to avoid humans (although others go to the opposite extreme and become super clingy). It's better for you to know exactly where she is in case she has problems during birth.

In the 24 hours leading up to labour your cat will probably stop eating and her temperature will drop a little. She'll go into the first stage of labour, but you may not even notice. It involves contractions of the uterus, but no visible straining by the mother.

The second stage is when you will notice the mother straining. The kittens will usually be born still contained within a membrane layer which the mother will most likely tear open and then she will start licking and cleaning around the kittens face to help clear the fluids so the kitten can breathe. She'll also usually chew through the umbilical cord and eat the afterbirth (the placenta is a greenish black color). Generally a mother cat will do a much better job looking after her newborn than a human can so give the mother a bit of time for her instincts to kick in. If she doesn't seem interested in the kitten at all then you may have to help out. You can break the kitten out of the membrane and put it in a towel. Open the kittens mouth and hold it face down for a few seconds to drain any fluid in it's mouth. Then start rubbing the kitten vigorously. Don't be afraid to rub it quite hard and vigorously to get the kitten to breathe. And be persistent. It can take quite a while before a kitten is breathing regularly. The amount of times I've had clients tell me that they thought a kitten was dead and put it in the bin only to hear it crying much later would amaze you! Once the kitten is breathing well, then keeping it warm is the next step. Hopefully you can just pop it back with mum and she will take care of it after that.

The intervals between the arrival of each kitten can be around 10 minutes to an hour. If it's over an hour between kittens, or the mother has been straining for longer than around 1/2 hour, then she may be having complications. At this stage I would recommend calling your local vet and possibly taking the cat in to be checked. Actually, once labour starts it's probably a good idea to call you vet to let them know just so they have a head-up in case any problems arise.

Once all the kittens are born it's a good idea to have both them and the mum checked over by a vet within the next 24 hours. The vet will check mum over to make sure that she is doing well and that there are no more kittens stuck inside her, and can check over the kittens for things like cleft palates.

Hope that helps a bit! Good luck!