Hey - congrats Alberto! You're gonna love it!
I did consider the B&W IR filter for quite a while though in the end I went with the standard color IR filter mainly because I'm used to it and I occasionally (ok, rarely) do a color IR... plus it's $50 cheaper and I need to buy the grip too. I've got a few killer Lightroom presets for handling the IR files and they are converted upon import so all I have to do is tweak. Plus the D80 has a very tweakable B&W mode built in that is pretty decent.
The D200, D80, & D40x all have the same sensor with slightly different processing associated with it. It's a good chip at ISO's under 400 and pretty decent up to 800. Though the D40x is clearly better than the D80, which has an edge on the D200 because of newer/better in-camera prcessing. But if you're shooting RAW they are more similar than different.
I found a used 5D $1,200 that I was gonna use but LP wants $500 for the conversion! Couple that with the Nikkor 18-70 DX being such a good lens for IR and you got yourself a no-brainer.
PS - If your D70 didn't come with an 18-70DX or you don't have one lying around, do your self a favor and buy one. That's the default calibration for LP with Nikon DSLR's anyway unless you paid for another lens to be used.