Yes, in manual or auto modes but not in i-ttl mode.
the current nikon speedlight range is thus: SB-200 SB-600 SB-800 SB-900 All will work with the Nikon D300s Older speedlights will also work, but without i-ttl mode.
yes
Yes in non i-ttl auto and manual
Yes it will. It will work in auto and manual modes. TTL does not work.
Yes in non i-ttl auto and manual
The price of a Nikon SB 400 depends from what location one purchases it. The average price of a Nikon SB 400 is around $130 and a used one is around $50.
Yes, It will.
The SB 800 is more powerful and has more features than the SB 600
The Nikon SB 600 is a compact and versatile Speedlight for expanded creative lighting control and remote flash photography. The benefits of using the Nikon SB 600 is precision flash control, auto power zoom coverage, and flash value lock.
The Nikon SB-800 is not compatible with Nissan SLR cameras. It is only compatible with Nikon cameras. One could damage their SB-800 flash unit by trying to use it with another camera.
Yes including: Automatic Balanced Fill-Flash (with AF Nikkor lenses/Standard TTL Auto including Programmed TTL Auto.