At the top of the page in this group, search for “Australia visa” in the search field. You’ll find many previous posts similar to your own, and lots of helpful advice. Good luck.
That depends entirely on what exact model phone you have and where in the world you are. Do a Google search using your phone make & model, your country and eSIM, and you’ll find lists of compatible devices.
Yes, of course, you can rent a car in Thailand using your respective American and/or Spanish driving licenses (the fact that you currently reside in HKG is somewhat irrelevant). There are limits to how long you can rent a car in Thailand using a foreign licence once you make that country your residence, by which time you should establish yourself with a Thai licence. If you want to get an IDP, you need to do this via your respective home country’s automobile association. I’ve read in this forum that the American AAA offers an online service, and I’m guessing there may be a similar service in Spain. Good luck.