1. I bought my 3/16in x 50ft amsteel blue winch rope from rockstomper.com. It was in the higher $40 range after shipping if I remember correctly. They were very friendly on the phone when I ordered mine. Have them throw in short piece of the abraision guard as well. It does a great job of protecting the rope.
There is a seller on ebay selling a 50ft piece for $36 shipped, but that does not include the abrasion guard. (ebay search - amsteelblue & amsteel blue)
Once you use the amsteel blue rope, you will never go back to a wire winch cable...
2. I have only used the Honda GN4 10W-40. This has worked great so far, but it does not stay -0F to 15F above where I live for any length of time. Maybe a few scattered days through out the winter here.