You are confused because you are afraid of making a mistake in your communication. We have all been there, especially after long periods of NC. Remember, NC is about getting your spouse out of a fog. You will not get your M back by staying NC forever.
You can reply something like "I'm great! Thanks for asking"
As for the library books, wth? A month late? Haha, make him pay the fine.
You can just reply 'Can you take the books back to the library? Not sure when I will have time this week'
Remember, he is asking the questions, not you. So it is not pursuing.
Me: 42 W: 32 Married 7 years together 8.5 S1: 7 S2:7 Bomb #1: 09-16-13 Recon #1: 11/13 A discovered 04-03-2014 W filed D 05-19-14 but never served me I filed D 12-02-2014 S 05-31-14 Divorced 5-19-16