That's a lot of characters.  I'll go through three of them. Let's start with Abigail Williams.  I think her motivations at first are to save face and cover for her "sporting" in the woods with the other girls and Tituba.  I think Abigail's motivations change though as she realizes that people believe the witchcraft accusations.  Abigail gets a huge sense of power about her.  She is able to control the girls around her, she is able to shape community belief, and she is put in a position to get rid of Elizabeth Proctor. With Elizabeth gone, John Proctor will suddenly be an available widower.  Miller makes it clear that Abigail has her eyes set on being with John.  

Mary Warren's motivations are easy.  At first, she likes the attention and feelings of importance that she gets from being an "official of the court." 

You must see it, sir, it’s God’s work we do. So I’ll be gone every day for some time. I’m - I am an official of the court, they say,

Later though, I think Mary is genuinely scared of Abigail's power and doesn't want to end up on the wrong side of it. 

She’ll kill me for sayin’ that!

Reverend Parris is a man that is obsessed with his reputation.  For him it was appalling that his niece and daughter were caught dancing in the forest.  For some reason it must have sounded easier/better to claim witchcraft than admit the girls did it on their own free will.  

Abigail: Uncle, the rumor of witchcraft is all about; I think 10 The Crucible you’d best go down and deny it yourself. The parlor’s packed with people, sir. I’ll sit with her.

Parris, pressed, turns on her: And what shall I say to them? That my daughter and my niece I discovered dancing like heathen in the forest?

Abigail: Uncle, we did dance; let you tell them I confessed it - and I’ll be whipped if I must be. But they’re speakin’ of witch-craft. Betty’s not witched.

Parris: Abigail, I cannot go before the congregation when I know you have not opened with me. What did you do with her in the forest?

As for which characters I believe were actually practicing witchcraft, I do not believe any of them were witches.  I think the entire situation got wildly out of control because it played on people's fears.