If a wish list is set on private will friends posting a wish list book be able to see if it's being posted to the friends private wish list?...what if the private wisher is first in line?

If you are a standard member, you have the option to post directly to a Friend. So when I post a book, if any of my Friends are wishing for it, as part of the posting process I can choose it to go directly to a Friend or FIFO. I don't think having your WL set to private would interfere with that option. Having set to private just means that people can't look at your WL to see what you are wishing for. Hope that answers your question.