GMAT

You are advised to appear for CAT to seek admission in PGP in IIMs.

Yes, you have to give GMAT test in Australia.

Yes, any good university will ask for a GMAT score though there could be exceptions. Check Thompson Rivers University or Vancouver Island University, they don't ask for GMAT.

A 750 GMAT score, solid work experience with demonstration of excellent leadership skills, strong career goals essay and an overall strong profile should land up in top ranked business schools like UCLA, INSEAD, LBS, NYU, KELLOGG, etc.

For current PGPEX batch, GMAT cut off is 717.

No, only work experience won't do. For the current batch, GMAT cut-off is 717 and the minimum work experience criterion is 5 years.

Hello Abhimanyu,
You may refer the link below for the list of top management institutes in India :
https://www.shiksha.com/mba/ranking/top-mba-colleges-in-india/2-2-0-0-0

It is impossible to get admission into a "good" college anywhere in India for studying MBA without appearing for any entrance exam. So you need to give one or the other exam, clear all its necessary cutoffs and perform well in the interview rounds(if shortlisted).

This year CAT will be conducted by IIM Lucknow, check the IIM L website for further notifications.
For MAT - https://www.aima.in/testing-services/mat/mat.html
For XAT - http://xatonline.net.in/
GMAT - http://www.mba.com/india
Keep checking these websites for registrations and online application forms.