Do you think Amber planned to take Johnny's money the whole time?

The money!

They fell out of love. It was a toxic relationship on both sides.

Definitely
I think she siphoned his Bank account whilst they were together

If Depp had stayed with his first wife and she took (hypothetically) him to court and lost, the headlines would be 'Paradis lost'.
Amber Heard was a trophy wife. Depp's mistake was that he didn't move on to wife 3 after HIS own shelf life as a sugar daddy was nearing expiration date.

She is a gold digger and used him to go on top in Hollywood. She saw rich old movie star showing interest in her and started showing interest in him, convincing him to dump his aging partner. Once she hooked him and got relevant and semi-famous she suddenly saw that he is old ugly, stinky, sad, pathetic alcoholic and user. He probably pretended to be semi-hot when they started dating. Kept himself in some sort of shape. And she didnt expect this downgrade so fast.

And she started being annoyed by this. She was young and pretty and he was old, ugly and stinky. And she is sociopath and decided to be bitchy. And he started to be bitchy in return. Because he thought he got ordinary gold digger, the one who will lovingly stare in his old eyes and tell how hot he is. Instead he got crazy sociopath who was ridiculing his old ass and being disgusted by it.

That was the moment when both of them should have quietly split up and move on with their lives.

But she was too stupid and decided to ride that MeToo wave and become Serious Victim and be press darling. And started this whole nonsense which backfired into her face. And now she is broke, has no career and people hate her. And he returned to being old and stinky washed up movie-star. No one won, they both lost. And he would be still fine he he would not dump Vanessa for a young gold digger.