I took the TOEFL Home Edition the other day and got thirty points in the writing section. I wrote about 800 words in the independent task, and about 600 words in the integrated task. I got no penalty for exceeding the recommended word count. Is that clear? You can write as much as you want. There is no penalty!
For what it’s worth, I did not write a conclusion in the integrated task, and I mentioned reading details first in each body paragraph (before the lecture details). Those approaches are fine too.