एक कदम आगे बढ़ाना

Not necessarily, but it implies the step is meaningful. You wouldn't use it for walking to the fridge, but you would for starting a new diet.

Yes, 'उसने एक कदम आगे बढ़ाया' (He took a step forward). Remember to use 'ne' with the subject.

'Badhna' is 'to grow/advance' (intransitive), while 'badhana' is 'to make something advance' (transitive). Since you are moving your foot, you use 'badhana'.

Yes, it's common when encouraging friends: 'Ek kadam aage badhao, sab theek ho jayega!'

Usually, 'ek kadam peeche hatna' (taking a step back) is used for retreats or failures.

Yes, you can change the number to show the scale of progress, but 'ek kadam' is the standard idiom.

Absolutely! It's a staple in motivational songs about chasing dreams.

You can still use 'ek kadam aage badhana', but 'kadam rakhna' (to place a step) is also common for physical walking.

It's neutral-to-formal. It's safe for both a boss and a best friend.

Using 'lena' instead of 'badhana' because of English influence.

Yes, it's very common in tech news: 'This new chip is a step forward.'

Often, yes. Taking a step forward usually means leaving a comfort zone.

Just 'कदम बढ़ाना' (kadam badhana) is also used and means the same thing.

Yes, it's the primary way to talk about social progress in Hindi.