Hi! I've just read this fanfiction and, I must tell you, I've loved every part of it! Jack and James are more than my favorite pairing in Lost, to me they're like the best ship in every fandom I've known, so a friend of mine suggested to me to read this one, and here I am.
I think you described both of them perfectly, and believe me, I can't wait for more.
Great job! :)