Yes, there's loads of backstory. You can find it here: [link]
Yes, I used the Chapter Traits from the Marine Codex. They've got See but Don't Be Seen and Take the Fight To them. Disadvantages are Flesh over Steel and We Stand Alone. I'm planning to build the Starfoxes Seventh Company as well, whose traits will be See but Don't Be Seen and Cleanse and Purify. Disadvantages will probably be the same, but I haven't decided yet.