Macbeth Questions

Bring on the tough stuff - there’s not just one right answer.

The last scene in the play, where Malcolm blesses all who have fought nobly on his side and promises to punish all who helped the traitors, is eerily reminiscent of the first scene with his father, Duncan. Is this play commenting that it's just the nature of history to repeat itself?
Macbeth starts the play as a hero and ends up a tyrant. Does this mean there are no truly evil people and power corrupts, or just that some people have bad judgment when choosing heroes?
Lady Macbeth is often hailed as the source of Macbeth's evil, but she never talks about her own gain. Even when she should be all happy as queen, she takes her own life. Is Lady Macbeth just caught in fate here? Was she just trying to do the good thing by being a supportive wife? Is good in the eye of the beholder?
The three witches, the weird sisters, are also often blamed for planting the seed of treachery in Macbeth's mind – yet the root of the word "wyrd" goes back to the Anglo Saxon word for "fate." Does one only need to think a thing is fate to make it happen? How much personal agency does one have against fate?
The good of other characters seems magnified when called out against Macbeth's evil. If not for Macbeth, Duncan would've died an aged king, Malcolm would never have tested his mettle in battle, and Macduff would've just been a good, quiet Thane of Fife, not a warrior-hero. Does it truly take the worst of times to see the best in men's natures?