Onward travel and Visa.

I'm getting so much conflicting advice, hopefully someone here can set me straight,

Australian passport, arriving 3rd of September to bangkok international airport. One way ticket.

At the momment I have no Visa, will I get 30 days on arrival, or 60 days on arrival,

Can you extend for another 30 days, regardless of if I get 30 or 60 days on arrival.

Do immigration require an onward ticket, if so, does it have to be a plane ticket, or would something like a bus ticket, hat yai to Penang be sufficient.

I appreciate any advice, thank you.