Ok here's the deal as I see it..

If you want to connect the Nook to the internet via a n900 then I believe the way to go is to use the MobileHotSpot "app" provided by the N900. This is not an easy install so be careful. But I assume it is better than paying for the JokerSpot app.

Now if you want the two devices to talk I think the way to start might be to get adb on the N900,, I think perhaps a debian version of it could be put on the n900 then the two devices connected by a physical wire.

It might actually be possible to do both at once ...

My goal would be to use the nook as a thing for my car. So ideally I'd like to install bluetooth onto the nook then obd ii (car port) to bluetooth then wifi and gps (somehow) over MobileHotSpot and adb.

FYI there is also a obd ii to wifi device.

Really the issue at hand is that the Nook has better hardware Screen, multi-touch, and Processor wise, the n900 is better in every other way. Especially because Google is such a creepy company.

Another choice might be to put Fedora or Ubuntu on the nook and be done with it.