Short answers, pulled from the story.
Technically his surname was simply Doyle. Conan was a middle name, derived from his great-uncle Michael Conan, a distinguished journalist. After finishing school, Doyle began using Conan as a sort of informal second surname. When he was knighted, he was gazetted as Doyle, not under the compound form.
Holmes was partly modelled on Joseph Bell, Doyle's former teacher at the University of Edinburgh Medical School. In 1892, Doyle wrote to Bell directly crediting him as the source of Holmes's methods of deduction and observation. Robert Louis Stevenson also recognised the resemblance, writing to Doyle on the 5th of April 1893 to ask whether Holmes could be "my old friend Joe Bell."
Yes. In December 1893 he sent Holmes and Professor Moriarty over the Reichenbach Falls in "The Final Problem," intending to free his time for historical novels. Public outcry eventually brought Holmes back in The Hound of the Baskervilles in 1901, and "The Adventure of the Empty House" in 1903 explained that only Moriarty had actually died.
Doyle investigated two wrongful conviction cases. In 1906 he took up the cause of George Edalji, a half-British, half-Indian lawyer convicted of animal mutilation, noting that the mutilations continued after Edalji was jailed. His work contributed to the creation of the Court of Criminal Appeal in 1907. He also campaigned for Oscar Slater, convicted of murder in Glasgow in 1908, and paid most of the costs of Slater's successful 1928 appeal.
Yes. In The Coming of the Fairies, published in 1922, Doyle reproduced five photographs taken by cousins Frances Griffiths and Elsie Wright in Cottingley, England, in July 1917, and argued that those who suspected them of being faked were wrong. Decades later the photographs were definitively shown to be fakes, and both Griffiths and Wright admitted the deception.
It ended in a bitter public falling-out in the 1920s. Houdini staged a trick in Doyle's presence specifically to demonstrate that impressive effects could be pure illusion. Doyle refused to accept the explanation, insisting in The Edge of the Unknown that Houdini possessed genuine supernatural powers. Houdini became a prominent public opponent of the spiritualist movement, which made their positions irreconcilable.