एक अहम् भूमिका निभाना

Yes, 'महत्वपूर्ण' (mahatvapurna) is a perfect synonym and is also very formal. 'Aham' is slightly more concise and elegant.

Yes, in Hindi, the word 'bhoomika' is always grammatically feminine, regardless of who is playing the role.

Yes, you can say 'उसने इस बर्बादी में अहम् भूमिका निभाई' (He played a key role in this destruction), though it's more common for positive achievements.

'Nibhana' sounds more like fulfilling a duty or relationship, while 'ada karna' sounds more like a performance or a formal act. Both are interchangeable here.

Absolutely. You'll hear it in every second interview where an actor discusses their 'character' or 'role' in a film.

You can say 'धुरीय भूमिका' (dhuriy bhoomika) or simply stick with 'अहम् भूमिका' as it covers 'pivotal' as well.

Only if the text is formal (e.g., to a boss). To a friend, it might sound like you're joking or being overly dramatic.

In Sanskrit, yes. But in modern Hindi, when used as an adjective, it means 'important'. Don't confuse the two!

A 'naganya bhoomika' (negligible role) or 'gaun bhoomika' (secondary role).

Yes, 'badi bhoomika' (big role) is a more common, slightly less formal way to say the same thing.