Shinbo fell in love with Ms. Shimizu and they eventually are living together. Shimizu was married but her husband spent all his time playing with persocoms and she was even locked out of the house. Whether she got divorced or is just having an affair with Shinbo, we don’t know. It’s just one of those example relationships that Clamp likes to put out.
2) Is Chii a Chobits, every one thinks she is, but it was never actually determined that she was.... ***SPOILER***
Freya and Elda/Chi were special persocoms created by Ichiro Mihara (same founder of Angelic Layer), who we never see his face, but it’s detailed in the manga. They’re more powerful than most since Icchan installed a special controller that if Chi didn’t find the person that was for her it would reset everything so that all persocoms would be incapable of finding love for themselves. The final manga volume explains how Chobits is an anagram for Icchan’s wife and apartment manager, Chitose Hibiya.
Other than that they don't really have anything particularly Legendary.
3) Not much was explained with the Cindacate or the appartment manager for that matter.......