I have some etiquette questions. Suppose you read a question that interests you, and you think you could write a helpful answer.
Is it your responsibility to read the answers that have been posted so far first?
If someone has already written a clearly-written answer that is in line with your own thinking, is it kosher to write an answer anyway, perhaps because you think your way of expressing it would be more useful for the OP or somehow better, or because you have more prestige in your paid employment or your publication list (and thus your answer might be more convincing and likely to give the OP peace of mind)?
Should you preface your answer with "I agree with So-and-so, and would like to add my thoughts."
Would it be kosher for the first answer writer to insert in the beginning or end of your post, "I agree with So-and-so, and would like to add my thoughts."
When I am deciding which posts I would like to upvote and downvote, am I supposed to take chronology into account?
I'm not posting a link to an example because I don't want to embarrass anyone.
Yes, you should read through the answers that have already been posted, as an answer that largely duplicates someone else's answer might otherwise be flagged for plagiarism.
You should post a new answer when you have something new to contribute to the question at hand. Just reposting the same information under the claim of having more expertise is a waste of time. If all you're going to do is agree with the answer, then you should just state that in a comment. However, if your answer introduces a new viewpoint or information that extends what has already been written, then you can certainly post that as a new answer.
If you're developing an answer that someone else has written, then you should absolutely cite that person's answer in your own. That will save you time and make readers' lives easier.
This took a while for me to understand. If what you mean is to ask if the original author can add such a statement if the new answer appears to be a riff on her older answer, then I think the answer would be yes, that would be fair.
This is entirely a personal issue. Stack Exchange doesn't place any restrictions or have any guidelines with respect to whether or not to consider chronology.