Loki

I'm sorry, but I don't know a website or book that could help you. However, orchestration is also very free. I recommend just reading the scores of the best composers (like the one in your profile pic) while listening to the music. In doing so you can get a general idea of what some ways of orchestration sound like. Compare that to the orchestration in more modern pieces, and you'll learn a lot.

I would personally start the piece with the bassoons playing the theme, and use the horns when it comes back later. The ending is quite abrupt, but the themes sound good, and there's some nice building up at 1:25.