Yes, the NavisWorks files have units in them: you can set the units value for all files in the global units and for all of the layers, sets and objects in your file.
One mode is single-threaded and second is multi-threaded, so you can switch.
Yes, but we will implement multithreaded rendering as soon as this feature is added in Visualize SDK.
Yes, in common way via Gi/Gs interface that placed in Kernel, also you can create your own, for example MFC or Qt application.
Files from Revit converted to NavisWorks have some Revit properties, for example categories and colors. So yes, we have an access to this data.
You can convert both to 2D and 3D pdf, this functionality is made by Visualize SDK.
No, currently we haven't such wrappers for BimNv.
Yes, we can extract text with BimNv SDK. We've got an example OdNwdLoad.exe to dump .nwd files.
We use ODA Viewer and OdVisualizeViewer to open and visualize. nwd, .nwc and .nwf files. You need following archives: Kernel, BimNv, Visualize and VisualizeQt.
Unpack and extract them into the same folder, go to exe\vc15_amd64dll sub-folder and run OdVisualizeViewer, now you can open a Navisworks file.