No salt at all in the sour dough. When baking you will add salt. I like around 2%. But in the mother sour dough you do not want any salt. This link is only about how to get your actual mother sour dough, not baking! That's still TODO and will follow up later.

Edit:

2% of the flour's weight in salt. Let's say you bake 700 grams of flour (500 grams flour, 200 grams sour dough) then you would add 14 grams of salt. Note please that this is my personal preference. It could be you prefer more or less salt.