honestly I think there would not be too much of a difference between the DJM900 and DJM2000 when setting up for traktor. I do not use Traktor but from what i tested in the past is the CDJ's are the sound cards for tractor so the mixer is irrelevant. just run rcas from the CDJ to the desired DJM channel and run the USB cables from the CDJs to your laptop
as far as LAN, the main difference is the DJM2000 has a built in hub so the decks can be plugged right into them via ethernet cables from the CDJs to the DJM and DJM to your laptop, also rca cables from CDJ to DJM which you probably have hooked up already.
If you are using channel 1 and 4 the CDJ's must be set to be player 1 and player 4 if you want "on air" to work.
If you use a macbook I believe you have to set up a "aggregate" device in your sound/midi area so the CDJ's are seen as sound cards
again, I don't use Traktor all the time so I hope any of this advice/info helped.
Please rattle off questions and ill do my best to answer sometime tonight