Youre really gettin into this stuff, neat...
I have no idea when 3 phase was first used commercially. I do know when it comes to motors its so much more efficient and self starting etc etc. At our plant any motor over 5 HP we tried to use 3 phase for lighter cheaper more efficient use.
I thought about joining the "Tesla Society" Back in the days he and Westinghouse and Edison really got into it I understand. I dont think things worked out that well for Tesla but he was a genius in his time. At Niagra Falls thay have a huge statue and a lot of history about him.
John T Tooo long retired EE but as I look back, ya know, "its been a good ride"