According to the sources I've found on a quick search, you should hyphenate 'coauthor', i.e., it would better be: "co-author".
no.
You do not hyphenate the number.
Generally co-author should be hyphenated, but the relaxed rules of modern times often present coauthor as one word
responsible
??
Dave and Larry wrote a book together, Dave is the main author and Larry is the coauthor.
coauthor
no.
The word coauthor is a noun. The plural noun is coauthors.
Don't hyphenate; ongoing is one word.
You hyphenate it only at the hyphen.
I think it's more accepted to hyphenate it.
You do not need to hyphenate.
You do not hyphenate the number.
Generally co-author should be hyphenated, but the relaxed rules of modern times often present coauthor as one word
Can you, or should you? You can hyphenate it if you're moving between lines in a paragraph and need to break up the word. You shouldn't hyphenate it normally.
You would hyphenate "thank you" when it is used as an adjective before a noun, such as in "a thank-you card."