हवा फिरणे

Yes, it works both ways. It simply means a change in the current state/momentum.

'Vare Phirne' is just a more formal/plural version. They are interchangeable in most contexts.

Yes, 'Hava badalna' or 'Hava ka rukh badalna' is the Hindi equivalent and is very common.

Literally, yes, but people will usually assume you mean it figuratively unless you are standing in a storm.

'हवा फिरत आहे' (Hava phirat aahe) is the most accurate translation.

It's a bit informal for a very strict email, but fine for a general update to colleagues.

There isn't a direct opposite idiom, but 'परिस्थिती स्थिर असणे' (situation being stable) is the literal opposite.

In this idiom, 'Hava' represents 'atmosphere' or 'luck' rather than just moving air.

Because the words are simple, but the figurative meaning is essential for understanding basic news and sports talk.

You can, but it sounds more like a literal weather change than an idiom about luck.