How systemless is this? Is it necessary to have the Blue Rose core book to be able to understand and use this? Is there crucial setting information not present here?
I think it works pretty well on its own. I'm just going from memory here. Tomorrow I'll try to remember to dig it out and reread it.
How Systemless? Pretty good. There are sidebars with feats and backgrounds, several NPC and monster stats all scattered around the book. The adventrue in the back is even pretty stat light.
I think you can get by with just the book. Blue Rose mainly has info on Alsid, the focus country, and so that chapter is the only one I would say you may have issues with. The chapters on the other countries are designed so that one can run camapigns from these countries which Blue Rose core book did not support.
If you hunt around and get lucky, you may be able to find the books cheap enough to warrent picking up Blue Rose and whatever the third book was. I found the 2 non core books for 5 bucks at my local store and bought them for a friend. And at Origins I know I saw all three at the discount booths.