Well, overtly, the ringworld exploration was because the galaxy was doing a number on itself. The puppeteers had already fled for an area that would keep them safe before the shocvkwave hit. they knew the rest of the races would sit around until the danger was imminent then do something hasty etc.... Nessus grabbed the two humans and a Kzinti that fit his bill. one human and Kzinti were to his thought direct results of the Puppeteer redesign of the species. Louis was the longest lived human I believe. So he was thought to be the most efficient survivor. The reason for the ringworld exploration was because the pupeteers were fleeing and their exodus was passing too close to it, so they wanted it explored for threats.
Ringworld had some undercurrents, where the Pupeteer homeworld was, the involvement of the puppeteers in human and Kzinti species. there were some further explanations and implications in engineers. But for the most part a lot of things were species level, not personal interactions. the closest was speaker to animal's response to Louis getting out of his crash balloon on the flying craft.