So this is what i did and worked on the first try. There are less steps ways to get it done but hopefully this clears up some of the confusion.
This also assumes you want the clouds and StockVisualEnhancements, it also assume you know how to copy/paste and extract zip files
Lovely mod, thanks!
Follow the link to download the main piece of the mod: https://docs.google.com/uc?id=0BwxOlKa6Lfl0b1UxaW1qTkxZZE0&export=download
Extract the zip file
Open the extracted folder which should be called SSRSS
Keep opening the subfolders until you are inside the GameData folder where you see all the actual pices of the mod DistanObject, Koprnicus, etc...
Copy all those files and folders in your KSP GameData folder EXCEPT PICK WHAT SVE YOU WANT IN HERE
OK, with that done go back to the SSRS folder you extracted everything to and open the EXCEPT PICK WHAT SVE YOU WANT IN HERE folder
Decide which level you want and open that folder
Copy the StockVisualEnhancements folder into your KSP GameData folder where just moments ago you copied the SSRSS main mod
You now have the basics installed, you need Sigma and the RSS stuff now
Sigma
Follow this link and download the zip file under the downloads section: https://github.com/Sigma88/Sigma-Dimensions/releases/tag/v0.5.0
Extract the zip file
Open the extracted folder which should be called Sigma-Dimensions.v0.5.0
Drill into the folder untill you see the Sigma folder
Copy that entire folder into your KSP GameData folder
One piece left and its just like the others
Following this link and download the zip file under the downloads section: https://github.com/KSP-RO/RSS-Textures/releases
I used the files under the v10.4 - Textures for RSS v10.6+ section. The bigger the number on the zip file, the better it looks
You only need to download one of them. If you want to see how they all look download them all, up to you
With your chosen RSS file downloaded, extract the zip file
You should end up with an extract folder with a number matching the one you downloaded
Same as before, drill into the folder untill you see the RSS-Textures folder
Copy that folder into your KSP GameData folder
That should be it. Fire up KSP and see what happens
HTH