I am at a similar stuck point as many others here have been. I've solved all the clues and filled the grid, found the co-writer and the phrase. But there are so many quotations to choose from and I don't have access to ODQ. Without the quote I don't understand the final step of adding letters or the extra letters in some entries (or the missing letters from others for that matter). I had hoped it might be the most well-known quote by this individual, but I can see no way to use that one to make sense of any of this.
Will continue to think until tomorrow, but if anyone is able to offer additional help before then I'm all ears!