Short answers, pulled from the story.
Andrew Johnson was impeached by the House of Representatives on the 24th of February 1868 by a vote of 128 to 47, primarily for violating the Tenure of Office Act by dismissing Secretary of War Edwin Stanton without Senate approval. The House adopted eleven articles of impeachment, most alleging violation of that act and that Johnson had questioned the legitimacy of Congress. He was acquitted in the Senate by one vote.
Johnson favored rapid restoration of the seceded states to the Union without protections for formerly enslaved people and without federal requirements for Black suffrage, which he viewed as a state matter. He vetoed the Civil Rights Act of 1866 and the Freedmen's Bureau extension, opposed the Fourteenth Amendment, and issued amnesty proclamations that allowed many former Confederates to return to power. Congress repeatedly overrode his vetoes and enacted its own Radical Reconstruction program.
Andrew Johnson became the 17th president of the United States following the assassination of Abraham Lincoln on the 14th of April 1865. Johnson had been elected vice president on the National Union Party ticket in 1864 and was sworn in as president by Chief Justice Salmon P. Chase on the morning of the 15th of April 1865, the day Lincoln died.
Andrew Johnson was born on the 29th of December 1808 in Raleigh, North Carolina, into poverty, and never attended school. At age ten he was apprenticed to a tailor named James Selby. After running away from the apprenticeship, he settled in Greeneville, Tennessee, where he established a successful tailoring business. He taught himself through reading and debate, married Eliza McCardle in 1827, and entered politics through the Greeneville municipal election of 1829, eventually serving as alderman, mayor, state legislator, governor, and U.S. senator before the presidency.
Yes, Andrew Johnson is the only former president to serve in the United States Senate. Tennessee elected him to the Senate in 1875, several years after his presidency ended. He died on the 31st of July 1875, five months into his Senate term.
The Homestead Bill proposed granting 160 acres to people willing to settle land and gain title to it. Johnson introduced it for the first time during his second term in the House of Representatives and championed it for years, driven in part by his own impoverished origins. He continued pushing for it in the Senate, where it was defeated 30-22 in 1859. The bill finally passed in 1862, after Johnson left the Senate to become Military Governor of Tennessee, and has been credited with opening the Western United States to settlement.