I have my own (just me) Pty Ltd business... had looked into sole trader instead but decided the extra hassle was worth it for me and my situation.
I'm happy to talk about what I understand of it all...
What do you want to know?
A Pty. Ltd. company requires a tax return at the end of the year, and yearly registration fees with ASIC.
so expect to spend around $500 to form the company, then maybe $800/year in registration and tax return fees with your accountant to run it.
The good thing about Pty Ltd is that you personally have limited liability - Even if the wheels really fall off this venture, nobody should lose their house (unless you've done something as a director you can be sued personally for...)
Since it's a thing with friends - you should still have a formal agreement as to who owns what of the business and how profits should be shared, and how you should work together and resolve disputes - just to put everything in black and white, in case things go weird one day.
Western Sydney Business centre has some really good advisors in my experience. They even run little regular courses on starting a business..
https://wsbusiness.com.au/On top of the courses, you get a few free consultation hours from them (gov funded) which can be useful if you have no idea what you're trying to do or why, in relation to the business structure or even developing the business. You might even get one of their consultants to talk to you prior to doing the legals side of the setup, if you want some more advice over which form is best for you?