1. I don't use Whatsapp so can't say
2. See 1
3. My favorite Cowlick!, also good Gleek, rowi, mehdoh
4. Nothing official
5. Only on Verizon at the moment, hopefully will show up on other carriers soon.
6. Press Power button + Home (Windows key)
7. No at the phone level, only within certain apps that have a setting for it.
8. I haven't messed with Xbox Music yet sorry can't comment.
9. I don't believe so just yet. Nokia has a Play To DLNA app on WP7.x so it's assumed that should be showing up for WP8 shortly as well.
You don't say what carrier you have but if you are on ATT you can use myATT for now as a data counter. It shows your usage. Apparently Nokia had one for the 900 but it's not listed as available for the 920 that I can find. I assume it will be at some point (or your carrier may block it preferring that you use one from them ).