Obviously you need to comment all class members, but javadoc is only required for the public interface - personally I javadoced everything except private.
For inheritence use the {@inheritDoc} tag (rather than @see) for body and all applicable exceptions wherever possible -
you should write the comments that are inherited in such away as they will apply to all inheritees ie don't mention implementation details in interface comments. You can always add to the above tag with specific implementation details.
Read the javadoc tool docs carefully for this tags useage.
Note the {@inheritTag} is a bit bugtastic at present