Yasuke is actually a fantastic choice as far as history/narrative goes.
A shame the game looks like more generic Assassin's Creed Mapfucking+Crowd Supermurder.
Which is fine if that's your thing, but I haven't been thrilled by an AC game since... well, AC1.
Yasuke wasnt a samurai, and he was only documented in Japan for 3 years. Most of the myth behind him is unfounded. He was a kosho which is a servant. It is notable he was allowed to carry a short sword if he needed to defend his master, but he held no privileges that samurai did.
Its not known if he died in Japan or left, as his master was forced to commit seppeku and he then was captured. Its noted that he was not killed because he was deemed to be a "beast", and in Japanese society back then it was considered shameful to kill a weaker enemy after capturing them.
I'm not sure where you got all of that stuff you wrote.