I don't think you have anything to worry about. Message #7 seems exactly right to me. I often travel with 2 passports, though the situation and countries are different.

As for entering the US as a US citizen, I often get a a couple questions--maybe because I'm an expat--they seem like friendly questions just designed to make sure I calmly have a story that agrees with their computer info. Sometimes US immigration gives me an entry stamp, sometimes not.