We do all of our AIR development for iOS on Windows, you'll need access to a Mac at the end to use Apple's tools to submit it to the App Store, but otherwise compiling from a Windows machine still works fine. It's easier to set up icons and launch storyboards using XCode on a Mac (AIR doesn't handle any of that for you unfortunately), but I believe there are ways to generate those files other ways.
AIR dropped support for 32-bit-only devices, so I'd say anything that runs iOS 11 or higher would be a safe bet for testing: we use an iPhone 8 and iPhone X as our baseline, plus an iPhone 12 Pro for phones, and also an iPad 5th Gen and an older iPad Pro for testing those. If you were just getting one device, I'd suggest an iPhone with a notch (X, 11, 12, etc.) so you can be sure you're handling all of that correctly.
Especially for GPU render mode which I think you also use, iOS is sooo much better than Android for that 😆 Apple devices from 2011 were performing just as good as newer Android devices for us, up until AIR dropped support for those old devices.