Short answers, pulled from the story.
Henry VI Part 3 existed by at least June 1592 as proven by Robert Greene's pamphlet registered on the 20th of September 1592. The play must have been written in either 1591 or early 1592 before theatres shut down on the 23rd of June to prevent plague outbreaks.
Thomas Millington published an octavo version titled The True Tragedie of Richard Duke of Yorke in 1595 under Peter Short's printing press. William White reprinted this text in quarto form for Millington in 1600 while William Jaggard included it in folio format during 1619 as part of his False Folio project printed for Thomas Pavier.
Edward Hall's The Union of the Two Noble and Illustre Families of Lancaster and York published in 1548 served as Shakespeare's primary historical source. Raphael Holinshed's Chronicles of England Scotland and Ireland from 1577 provided additional material though often reproducing Hall verbatim.
The stage would witness four actual battles plus one reported battle more than any other Shakespeare play. These scenes depicted the horrors of civil war rather than the glory of national unity during the Wars of the Roses conflict beginning in 1455.
Act 1 Scene 1 introduces Montague as York's brother-in-law representing Richard Neville Earl of Salisbury while Act 2 Scene 1 presents him as John Neville Marquis of Montague Warwick's younger brother. Productions resolve discrepancies by establishing one consistent figure representing Warwick's brother and Salisbury's son rather than two separate personas shifting identities mid-play.