Hi Peteradams,
Soft pastels are a type of very fine grain chalk. So, yes, they are chalky,
I, for one, don't recommend any grade of paper. Some do, and that is fine. But sometimes it can be difficult to get these, but other grades would be more readily available. So my 'recommendation' there is to get and use what you can readily get your hands on. It can be easy to get lost in technicalities. If what you can get your hands on gives you the results you are after, then there is no right or wrong.
Here's a link to the Melish Technique that I use for sketching white on black. You may already be familiar with the article:
[
http://www.iceinspace.com.au/63-614-...html]Sketching DSO's using the Melish Technique[/url]
At the end of the article there are a few resources to further assist with developing your technique and confidence. Do a few practice pieces to get a feel for the materials and how they respond. This will take much of the guess work out of attempting to do a first up sketch in the dark. If you have any questions, please ask. Any pieces that you produce, practice or at the scope, do post them,
Alex.