I would personally go with the set which is most 'user-friendly' for me. I went to test out Nikon and Canon cameras, and I didn't feel comfortable with the Canon cameras, so I went with Nikon instead. Each camera does have its pros and cons, but you should go with what 'feels best' for you.
Next, if you're just starting out, start with the kit lens. Familiarise yourself with shooting and everything, as well as your camera functions etc. From the looks of your post, you seem to be covering range. So why not get the 18-200mm VR (if you're looking towards Nikon), as it's a good 'walk-about' and rather 'range-y' lens? Also, you should head down to Nikon Service Centre (NSC) or the Canon Service Centre to play with their lenses they have there. From what I know, you would have to make an appointment for the Canon Service Centre. For NSC, you can just pop in any time to test out lenses, ask questions etc.
Also, when it comes to lenses, you should familiarise yourself with your lens as well. Like cameras, each lens has its pros and cons. Personally, if you're getting the D90, it comes with a 18-105mm VR lens. I think this is good enough for starters. I personally own a D80 with the 18-135 kit lens (my only lens thus far, cause I'm a poor student ><), and I rarely go beyond the 70mm mark... Of course, it all depends on what subject you are shooting. I notice that you're going for 50mm f/1.8 for all your options, which is a real fun lens used for portraits etc. That's understandable.
For flash wise, I think that the SB-600 is... lame... I own the SB-900, and have used the SB-600 before as well. SB-600 is good for starters, but in the long run, maybe you wanna invest in the SB-900. Not too sure about Canon, cause I rarely use it.
If I were you, I would go for B or C, although I'm a Nikon user. Maybe it's because for A, the 18-70mm is only average and the 70-300mm is not worth the money in my opinion. But like I said, test out the cameras and lenses you wanna buy. The most important thing is to 'have the feel' when you're using your camera. What does it mean to 'have the feel'? You'll know when you pick up the camera.
