Restoring my 1979 Mercedes-Benz S-Class W126 - Where to start with the interior?

I recently acquired a 1979 Mercedes-Benz S-Class W126 and I'm excited to restore it to its former glory. Now that the exterior is undergoing cosmetic repairs, I'm focusing on the interior. Where should I start with the original upholstery, dashboard trim, and electronics? Are there any specific products or techniques you'd recommend for preserving or replacing these components?