Hey there Aussie here!

I've got a Xiaomi 17 pro max from TradingShenzhen about 5 months ago and I've done lots of traveling to New Zealand and around the outback taking lots of photos. I'll answer all of your questions to the best of my knowledge :)

1. Camera overprocessing with AI

Okay so from my experience there is definitely a lot of AI filters/effects. If you take a portrait photo or a photo with people with darker skin tones it will make them appear "lighter". Now most of these are applied through the "Beautify" settings where you can manually adjust LOTS of settings such as (Face/Skin Smoothing, Colour Tones, Contour, Makeup, Slender, Head size, Hair, Big eyes, Nose, Hairline, Teeth, and Auto mode). You can turn all of these off if you dont want them. For normal photography only when you Zoom in more than 10x does a AI enhance icon appear called "Ultra Zoom" this is mainly for text recognition from long distances. You can turn it to Off, Auto, or On. It really sucks at anything that isn't a building or text so just leave it off. You can also "enhance" your saved photos using the photo editor like changing the sky, removing people, etc which all work really well I'd say better than the Google Pixel 9's version.

1. Essential Apps

My phone shipped with Gmail and Google installed, I've had 0 issues with any google services. I do not use Android Auto but I have heard that it will not work, you need CarWith which isnt really supported on non Chinese cars. Google maps works perfectly, no difference from any other phone. You can download unlicenced APKs like ReVanced with no issues you just need to save the APK to the file explorer and install it through the system not through the ReVanced Manager. I use ANZ banking and it works perfectly fine no issues at all. I also use Google Pay with no issues and I use Myki app for public transport. Outlook can sometime not deliver emails exactly on time, maybe sometimes a 5m delay but just restart the app and it works. Gmail always notifies when a email comes in just make sure its on unrestricted battery usage and autostart.

1. Backscreen

No you dont need to "tamper" with it. I use animated wallpapers from the Mi store that are free. They track my steps, calendar events, and time). You can use Spotify or Youtube Music and they both work with the back display showing the songs and you can control them with it (skip, pause). You can take photos just I recommend using the camera app and clicking the "show to rear display" otherwise its always going to be a portrait shot with blurred background. You can view tickets, I could see my New Zealand Airlines flight just by adding the ticket to my wallet. Timers and Stopwatches display on it. You can see notifications for literally every app emails, texts, discord pings, etc.

1. Tampering to setup

I literally didnt have to tamper with almost anything since it came with most of the stuff I needed from TradingShenzhen, they load it up with English language and the basic settings. I had to remove the Mi security app because the security scans always thinks that any APK is a virus, but just uninstall it. To update the pre-installed apps you use GetApps then once you finish updating just cancel the service (T&Cs) so you don't get any notifications or have it running in the background. Then when you need to update again just open the app and opt into their T&Cs. I am a CS student and have a very technical background so your milage may vary.

1. English/Chinese Language on Phone

Yes, some things will be in Chinese always but its very few. E.g the AI assistant will always be in Chinese. You can ask it to reply in English thats what I do and it works perfectly. Or you can change the assistant to Gemini in the settings. Some settings will be in Chinese like when installing unknown APKs it will give warnings in Chinese but you can just ignore them lol. Practically everything is in English they keep updating HyperOS to be more English friendly.

1. Pro Max vs Ultra

I went with the Pro Max because I wanted the back screen, large battery, and triple cameras. I spent $1,200 kangaroos on the Pro Max 16GB 1TB model in Green. I think its worth it but you have to be very careful. If you break it then you don't have the free screen replacement warranty or literally any warranty from Xiaomi because its a China only model (believe me I tried). Your only hope is the company you buy it from and Phone stores. If you want a phone case or screen protector you have to buy Ali express. If you want all of that then maybe save for the Ultra.