My understanding is that the Lightroom "defaults" are just a representation of the RAW data with minimal adjustments. I have the uneasy feeling that this could open up the sort of discussion that turns ordinary folk into complete w*nkers, so I prefer not to go there and just start with what I see when a Raw image is opened and go from there (except I almost always have to lower the blacks in the "basic" panel).
I remember being slightly distressed when switching from jpegs to Raw to find there was no "right answer" to all the things you mentioned, but I had to decide for myself. Now I find that quite cool, and Lightroom the least of my worries.
If you find yourself doing the same things to similar photos in the develop module, you could save that as a preset and make that your starting point. You can easily undo it in the history tab. Some people do this on import, but if they want to go back to a "zeroed" setting, I think they have to re-import (i.e. they're in the poo).
A round-about way of saying if you want to mimic the D300 processing, find out what works and save it as a preset.
Try shooting in Raw+jpeg and import and compare both images. Try opening a RAW image in another developer and compare it to Lightroom.
Cheers, David