1. He was originally married to a daughter of Hojo Gen'an (who adopted him), as part of an allience. This seems to have lasted maybe a year, as when he went to Kenshin a year later, he was given Kagekatsu's second sister as a wife. There was a daughter from the first marriage, and two sons and a daughter from the second one. Busy man!
2. The theory that Kenshin intended to split his inheritence between Kagetora and Kagekatsu is modern. The theory is that as Kantou Kanrei, Kagetora was to be in charge of the Yamanouchi Uesugi, while Kagekatsu would be in charge of the Echizen holdings. This makes sense, since the Yamanouchi and Echizen Uesugi branches tended to feud a lot. With his ties to the Hojo and his holdings in the Kantou, this would put Kagetora in a very solid position.
3. There is a theory that Hojo Ujihide and Uesugi Saburou Kagetora may be two different people, since at the time when Saburou went to Kenshin, Ujihide was in Edo.
4. Otate may have been a castle more than a fortified residence. OTOH, I'm still not convinced that Wiki is a totally accurate reference, so... Other sources I have read say that it was an administrative center. Given its geographical location relative to Kasugayama-jou, this would make more sense than a castle per se. Perhaps it was more like a fortified residence. Though I would expect that in the case of attack, anyone of importance would retreat back to Kasugayama-jou proper.
For reference, Wikipedia lists his date of death as 1579-4-19 (Tenshou 7-nen, 3-24). It says that he committed suicide at Samegao, so there is reason to suspect the accuracy of this date of death.
I think this is the book on Uesugi Saburou Kagetora that I saw once about a year and a half ago and decided not to pick up because "I'm not that much of a fangirl." Important notes to self: 1) I am too, and 2) given how freaking hard it is to find books on the guy, pick the darn book up!!! Sheesh. I haven't even been able to find this book on Amazon Japan or even *in* Japan.
Edit: Ah. Reason I can't find it is I'm looking in the history section. It's a historical novel. Eh, for $12, I'm willing to give it a try -- providing I can actually find it.