WW got the answers to all the rest of the questions so no need for me to repeat.
Here is the sauce on Shakespeare on how he researched his historical plays.
Sources of Shakespeare's History Plays
Most of the Bard's English history plays, as well as "Macbeth" and "King Lear" are based on Holinshed's "Chronicles." Shakespeare was known for borrowing heavily from earlier writers, and Holinshed's works, published in 1577 and 1587, were a key reference for Shakespeare and other authors of his day, including Christopher Marlowe.
Interestingly, Holinshed's works were not particularly historically accurate either, but instead are considered mostly fictional works of entertainment. If produced in the modern day, both Shakespeare and Holinshed's writings would probably be described as "based on historical events" but have a disclaimer that they were edited for dramatic purposes.