Anonymous participant 822 using cash is always best. Always have multiple bank accounts back home or in different countries, never rely solely on Thai bank accounts.
Yes. You can transfer funds to Thai bank accounts instantly for USD 5. Scan pay is available, though not sure if personal accounts work. Their debit cards are reliable and the account currency is USD, the world's foremost reserve currency.
Cambodian bank accounts need to be opened on ordinary visas, valid for at least 6 months. This is easy to do...just enter on an ordinary visa (best to get an e-visa) then extend for 6 months through an agency then open your bank account in person.