1. It is unlikely the immigration officer will ask you for proof of finance, but they could.
2. Proof of finance has to be in cash. Can be any currency, so A$ is fine.
3. The ATM withdrawal fee in Thailand is 220 THB (about A$10) if you use your Australian bank debit card to withdraw cash in THB. Your Australian bank may charge you fees as well.
4. The best way is to bring A$ cash and exchange to THB at SuperRich in Bangkok City centre. You can check the live exchange rate from their website below.
SuperRich (Green)
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Location in Bangkok City centre:
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(Rajdamri 1 Rd)
5. Unlike Australia, Thailand is mostly a cash economy. Most smaller stores accept cash only. Credit cards are accepted at supermarkets.
6. The best Australian credit card for travelling is 28 Degrees MasterCard. No annual fee. Very few fees compared to other credit cards. Get it before you travel.
7. The best travel insurance for Australians is Southern Cross Travel Insurance. Travel insurance is an absolute must when you travel. Overseas medical care, if you need it, can wipe out your life savings.
8. Google Translate app is a must. Download Thai language so you can use it even when you don't have Internet connection.
9. Don't wear jewelery when you travel. Don't make yourself a target of snatch thieves and robbers.