Your punctuation and grammar look fine to me. You could have omitted the comma before 'so' in the last line but it's alright to have it there.
Re the comma you've seen before 'dependent' clauses (= subordinate, I imagine?), maybe you could give a few examples from the book you quote.
Offhand, I can think only of what are called "non-restrictive relative clauses" e.g. The teacher reprimanded the children, who had behaved very badly. It's a stupid sentence, I know, but I can't think of a better one.
If there hadn't been a comma after children, then the teacher reprimanded only some of the children: the ones who had behaved badly.
The presence of the comma after children indicates that you're talking about the whole class: all of them had behaved badly.
This is only one type of non-restrictive relative clause but they all require commas.