Hi there! Welcome to Android!
1) Depends on where you bought it. If it's from the Apple store, it will only transfer the files that have been downloaded to your phone. For the rest, you'd have to download the MP3 files to a computer or SD Card and transfer to your phone manually or using a 3rd party app to sync with your desktop music (Smart Switch can also do this on your PC, assuming all tracks have been downloaded).
2) Not yet. Nougat update for carriers is expected in Q1, however, so it shouldn't be long.
3)I'm gonna be a bit 'broad' on this one: Turn off anything you don't need (NFC, WiFi Direct, BT, etc.) and use auto-brightness. You can always use the Battery Saver features if you're in a pinch, but that will limit a lot on your phone. If you can stomach it, you can set your screen to a lower resolution to save battery, but you do lose crispness and detail on screen.
4)I prefer Chrome just because it lets me sync with other devices and I can switch from computer to mobile and to tablet and not lose my browsing.
5) I've been using my Edge without a screen protector for a month now since the one I had (thin film) just started to peel off after a few days at the beach and the screen is scratch-free so far. BUT you do have to be careful. Sand, especially, will scratch the glass easily with the right grain and the right spot and the right rub. Glass protectors are worse on the Edge, but they do protect the S7 better, but most will have a 'halo' around them because of the slightly curved edges on the S7's, well, edges.
6) Anything Apple will be hard to 'port' to Android, and of course, you'll miss iMessage. But other than the latter, you can eventually port and substitute Apple's services. These might help.
How to get your iTunes music onto Android | Android Central How to transfer contacts from iPhone to Android | Android Central