Just make sure you get a supporting letter from your doctor or hospital attesting to or confirming that you are undergoing long term treatment so that you can present with your DTV application
You need to report it stolen at all 3: Aust embassy, Thai immigration and Thai police even via the Tourist Thai Police, if a resident in Thailand, Immigration will advise what you need to stay in Thailand without a passport and naturally apply for an emergency passport so that you can return to Australia but without a valid ordinary passport you won't be able to fly anywhere
no, I was told by immigration at the airport in BKK that the visa is valid for 180 days so if you enter 1 Sept 2024 you are allowed entry for 180 days or approx 6 months and you can come and go as you please within those 180 days but a new 180 days does not kick in every time you re-enter the country so you enter the first time you get 180 days after which you must leave and then re-enter for a further 180 days for the validity of your 5 year DTV visa
My understanding is that the visa is valid for stay up to a max of 180 days with multiple entries during those 180 days after which you would need to leave Thailand and re-enter for a further and successive 180 days etc up to the validity of your visa of 5 years.