Hi,
How's it doing. If it appears listless mix a small amount of glucose in warm water and drip it into its mouth. I have rehabilitated quite a few different wild animals and although you may want to cuddle it, try not to. If you plan to release it when its old enough, you dont want it to think human's are friendly (cos most of them are not).
I raised a baby pigeon(called Percy!) i released him but he was attacked by a cat, luckily he came back to my bird table and I took him in again. He is now living in the wild but he comes back twice a day to feed. I know most people think pigeons are vermin but he deserved to be given a chance.
Keep us up to date with the squirell.
Oh regarding the milk, you can buy dogs milk from most pet shops. Its called lactade and will be much better for the squirell