Some websites block access from overseas IP addresses for security reasons (e.g. fraudulent transactions, denial of service attacks, etc.).
To access these websites, you need to use a VPN (Virtual Private Network) service that connects you to a server in the country that is allowed to access the websites.
For example, to access the websites you mentioned, you need to connect to a VPN server in USA so that your IP address is from the USA. That way, the website thinks that you are accessing the website from USA.
I have been using NordVPN for 3 years for exactly this reason - so that I could log in to bank websites, retailer websites, etc. in my home country.
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)
*****************************
Location in Bangkok City centre:
*************************************
(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.
2. If you are asked to weigh your backpack, your waist pouch or small sling pouch is not going to be weighed.
Feel free to put things in your waist pouch or sling pouch to reduce the weight of your backpack.
You can also carry or wear additional clothing to reduce the weight of your backpack. Your pockets are also useful for this purpose.
3. Since you do not have checked-in baggage, you won’t be able to bring any sharp or pointed objects with you (e.g. razor blade, scissors, etc.). If you bring them, they will be confiscated at security checkpoint.
Same reason why you didn't provide (1) a website link to the official source of information in your first post, (2) exact address of the immigration office to extend stay, (3) exact operating hours of that immigration office... 😉