You should remain in the country you applied in until the process completes. Thai embassies view the evisa system in the same way they did when you physically had to hand over your passport. The only thing that's changed is how you apply. Many embassies want to check you remain in the country they are responsible for and check just prior to issuing the visa, don't risk losing the visa due to your impatience
Anonymous participant Melbourne means you apply via Canberra. Sydney only serves NSW. 9 days is highly unlikely to be enough, both quote 10 business days processing time although there are reports of it being much faster in Canberra. However if you are not an Australian citizen you need a Vevo to apply
Leave AI alone, it's notoriously bad at this sort of thing. If you want to retire in Thailand there are at least 5 visa options available to you, each with different criteria, requirements & and validity periods
Being a remote worker is not enough. You need to work remotely FROM Thailand and your employer needs to give you permission to do that along with a statement that you won't work for or interact with clients inside Thailand
probably best to think of it as the extension just carries on until it's permitted date whether you are in Thailand or not, assuming you get a re-entry permit
yep you can do that, either a single re-entry permit or a multiple but be aware it doesn't add any time, just keeps your entry stamp alive when you leave
you don't need a criminal police check for an extension of stay. Depending which visa you apply for you may need one but that's most likely in your home country before you travel to Thailand