How did Gorbachev know not-so-totalitarian alternatives, and new economic relations?

He apparently knew of them primarily through the prism of the Soviet intelligence system and from the viewpoint of one who grew up in the Soviet Union.  He did not have the interior perspective of one who is or has been in a leadership position in one of the western societies.  He knew the problems of Soviet society up close and personally but knew the west from afar.  That was inherent in his situation.

I agree that the demise of the Soviet Union, when and how it died, was largely the result of Gorbachev's actions.  I do not think it turned out anything as well as he would have liked.  He certainly put his own position and the future of his family in play and is probably fortunate to have emerged as well as he did.  I give him credit for having the courage to push his society in the direction of greater openness and of detente with the USA in the face of great uncertainty.

Meanwhile, Reagan was posturing for public approval with his "evil empire" rhetoric and doubling the national debt of the USA with military spending.  I think Gorbachev saw that neither side could win the Cold War militarily, while the Republicans in the USA claimed that this is exactly what they had done.  Point Gorbachev.  Absent a credible geo-political rival, US triumphalism under "W" inflated to gigantic proportions and then proceeded to pop, like a giant bubble gum balloon, all over our face and society, unfortunately smothering the world economy in the process.

Gorbachev could have elected to "stay the course" and try to keep a lid on change in Soviet society.  Hard to know how that would have worked out.  He could have taken a course more like that of China, but I think that is what he had in mind when overtaken by events.  The Chinese undoubtedly found the Soviet example instructive.  I think what Gorbachev needed was better domestic rivals and a way to slow down the process.  A sober Yeltsin might have helped.  The USA was fortunate at its founding to have a number of first rate players and the luxury of time in which to hash out a 2.0 version of our government.

I watched these events from afar and through English language coverage.  I do not know your reasons not to cheer anything Soviet, but you appear to have had a closer perspective.  

"It is not necessary to have hope in order to persevere."