A. There should be no problem (there is a limit, I think, but 40 ft should not be a problem.)
B. Don't know.
C. Sounds like a lot of hassle. Have you considered getting a wireless router? A bit of an investment, but you can then move the pc around as much as you like, without having to worry about the location of the socket box, and add additional PCs later on if you want. (Or get a laptop so you can surf in the garden)
