1) Haikasoru finally has a twitter account (here).
2) Mardock Scramble is going to be all three of the original Japanese books in one (it’s over 500 pages~ [Amazon and Simon and Schuster both say 680!!]).
Side note that the first anime movie adaptation is going to premiere this weekend at NYAF/NYCC, and the author Tow Ubukata will be there!
3) Mirror Sword and Shadow Prince is indeed a sequel to Dragon Sword and Wind Child, the reprint of which is under the Haikasoru line (and has a nicer cover than the non-Haikasoru version that I have).