1. Idk. I take good care of my phones because I’m 31 and not a perpetual teenager who thinks their stuff is unbreakable, so I go without extra insurance. (Not that I think you are, just sayin’.)
2. Multitasking isn’t a thing on iPhone. YouTube will still shrink to a window, but say goodbye to splitscreening two apps. Otherwise, smooth transition. File management is the only real downside. Also, the keyboard is the biggest adjustment. You really don’t get an option. Even other keyboard apps will use the same iPhone style keyboard design, so apps like Swiftkey are pulling support for iPhone because it’s just not the same experience you get on Android.
3. I use Soundcore Space Q45 and Samsung Galaxy Buds Live for headphones. They both work fine. No issues. iPhone doesn’t have aptx or LDAC though, so you won’t get the highest fidelity in Bluetooth. That said, Bluetooth headphones still sound good so it’s whatever. No issues with connectivity.

I just swapped recently from the Galaxy Fold 3, and before that, had Sony’s Xperia 1ii. The best Android feature is hands down the multitasking. Having two squared apps on the Xperia 1’s 21:9 display and more than 3 apps on the Galaxy Fold 3 was killer in my opinion. I’ve used more than 2 dozen phones in the past 10 years, constantly trading, selling, and buying devices. Android is the king of PC-familiarity, and since Apple wants to distance themselves from Windows (understandably, they’re Apple), we’re never going to see the iPhone have multi-app functions.