Shadows question

First of all, have you read Shadows yet? Obsidian WAS released before Shadows, so you could definitely read it after Obsidian. I read it after, and personally, i would recommend doing it. You pick up on things that are talked about/hinted at in Obsidian. Plus, it takes place before Obsidian, so you can see how much things have changed in between the two books. But, it would also have up-sides to reading Shadows first, like how you know what happened to certain characters and it gives you insight on characters. Either way, it's up to you.

You could ready it after Obsidian. I personally read it before as in Shadows-Obsidian-Onyx order, but the 'background' knowledge that you get in Shadows doesn't really play a big part in Obsidian. That said I would recommend that you read it before you move on into Onyx...which is a must since it's absolutely amazing!!!
Hope this help

Either before or after book 1 but I do suggest reading it before book 2 because it kinda ties in with book 0.5 (Shadows)

I read all three and then read Shadows and really enjoyed it in that order because after you read the third one you are depressed and Shadows makes you feel a bit better

I read it after Obsidian and it was fine. but i did clear up a few things