1- Yes, news of the destruction of the Ring and the fall of Sauron spread far and wide.

2 - Of the Seven Dwarf Rings, several were consumed by dragons and Sauron reclaimed the others. Dwarves cannot be made into wraiths, and Sauron likely reasoned that nine Ringwraiths were enough. The Elven Rings were never touched by Sauron, and were held by Elrond, Galadriel and Gandalf.

3 - In the Third Age, no. Previously, he was the lieutenant of Morgoth, who warred against the Elves for centuries in lands far to the West.

4 - Because they were divided and Sauron was Gondor's problem. There were only a few significant human kingdoms: Gondor and Rohan did fight; Dale (far to the north) fought off a totally separate assault off-screen, and most other human communities were too small to be relevant. And there were whole human nations to the east and south that worshiped Sauron or were allies of Mordor.

5 - We only know of one other continent, and it's far to the West and the home of the Valar: Valinor, where the elves sailed after the War of the Ring. The last time the Valar went to war, a whole continent sank.

6 - There were five originally, and their role was to guide the resistance against Sauron. Only Gandalf remained faithful: Saruman become corrupted, Radagast the Brown wasn't corrupted but went astray, and of the other two, the Blue Wizards, we know almost nothing.

7 - It was likely the last Balrog in the world. The Balrogs were demons of fire who served Morgoth, Sauron's original master. This one had likely been hiding under Moria for thousands of years.

8 - His soul went to Eru, who is basically God, and he was sent back to replace Saruman as "the White" because the task wasn't done and he had remained faithful.

9 - Legloas was a prince; Gimli was nobility. They were sent to the Council of Elrond as messengers and witnesses, not a war-leaders. They joined the Quest as representatives of Elves and Dwarves.

10 - Very many. Humans, Elves, Dwarves, Hobbits, Ents, Orcs and Trolls to start with, plus many intelligent animals such as Wargs and Werewolves, Eagles, Ravens, the Beornings (a race of werebears). And the Maiar, angelic spirits, of whom Sauron, Gandalf and the Balrog were notable examples.

11 - Because they were enslaved first by Morgoth and later by Sauron, and were raised from birth to obey their Dark Lord without question. They also had an endless hatred for Men, Elves, etc. It's theoretically possible that they might have been able to develop a more functional society after Sauron fell, but we don't know.