1) Stores which normally carry japanese language books including manga and light novels might carry it --- e.g. Kinokuniya Bookstores.
amazon.co.jp (nasty shipping costs) and yesasia.com (shipping is cheap but they're flaky about stock-in-hand) are alternatives.
2) There are no *licensed* English distributions of the novels or the more recent manga announced as yet. There *is* a hobby-translation of the light novels in progress with different team members taking on various chapters or volumes. There will probably be scanlations of the manga but the first volume of the manga only got released a few weeks ago. There is also the magazine that runs the monthly comic (which started up last September).
3) The first season is a condensed form of Volume 1 and 2. Volume 3 picks up just after the conclusion of the series (though a reader would miss a lot of the story detail if they just went by the anime and Horo would be sad
).
meh... serenade wins the simul-post contest .