From messing around with some of this and watching the twitch stream Brad was on 5/13 it goes something like this
Number of stars effect the number of planets
The number of planets effects the number of habitable and extreme worlds
The XML shows factors to apply be each of these things.
So you can create a new game and go into the debug console (~) and type "fow" with no quotes. Make a note of the galaxy, then exit, change the parameters and start a new game and open the fog again to see the differences.
Stars scale to the map size as well from the looks of it, which makes sense.
Hope this helps.