I recently setup a cheap guiding system using a viewfinder and this is a bullet-point list of how it works. It describes one of the two scenario that you mentioned, I am not sure about connecting the camera to the mount:
- The webcam connects to laptop.
- The mount connects to laptop as well.
- Laptop is running PhD or Metaguide or some other guiding software.
- PhD analyses the webcam images and sends guiding corrections to the mount.
You do not need Backyard Nikon for guiding. However, you should be able to use it for dithering. Dithering means that the image is slightly shifted between each exposure. After each exposure the imaging software sends a dithering command to the guiding software which then adjusts the mount.
Dithering improves image quality significantly, especially when a DSLR camera is used. I would say it is a must once you get the guiding going. You just have to enable the option somewhere in the software.