1) sun_color isn't passed to the shader, but you can easily amke it so that the material values are set to the sun_color every frame. Just open the NM.wdl, go to the mat_NM_event() and add vec_set(mtl.specular_blue, sun_color);

2) Stencil shaddows worked just fine for me...

3) I thought I left out the attenuation on sunlight. I'll do some testing. Also, the large faces your using for testing, are the just faces, or actaully shapes. The vertice normal are interpolated, so the edges might think their facing away from the sun...

4) Static lighting only works when their are blocks to read the lightmaps from. Only stencil shadows will work. The shadows are not controlled by the shader at all. stencil shadows also pass through objects, so use them carefully...