Good luck with finding the correct outfits etc.
My advice would be this:
Think carefully about the image/period that you are trying to project. Do you want to look like a mid 20th century Australian, or an American of the same period? (or even a Frenchman etc, come to that)
Look through books of photographs and familiarise yourself with the period. If you are thinking Melbourne late forties early fifties - look at local history section in your local library. Go through the photo albums of your parents/grandparents etc. Old family photos are great for genuine inspiration.
But also question yourself: Does a particular style work for your body type?
If a wider trouser dwarfs your feet, consider narrower trousers (personally I like wide trousers because I have always been self conscious about my feet). Compare various hat brim widths - which one suits your face. Don't just go for a fedora because of the obvious period connections. It may be that a narrower brim is much more flattering to your facial features.
I note that you mention casual trousers worn with contrasting jacket as a look you like. You are in Australia - ask everyone you know if they or any family members used to play cricket and have some old cricket whites hanging around the house. Not the modern abominations, but the classic white/cream flannels. They are the perfect for wearing with a contrasting jacket.
And don't ignore the missmatched suit jacket with non-suit trousers. I don't know about Australia, but in the UK that was a very common look in the mid-20th century. Get the colours and fabrics right and it can look very good.
Look forward to seeing some photos once you have started to build the wardrobe.
Final piece of advice - keep a regular watch on the 'classifieds' and 'vintage finds and deals' section. Something will turn up. Post your chest and waist size in this thread - you might be lucky and find someone has got the perfect jacket/suit/trousers just waiting to sell to you. Remember, there are plenty of people reading posts even if they don't reply.
Best of luck.