1: Besides a memory card, music could be transferred over the network - this would involve sharing a folder on your Mac, then browsing to it from the Windows desktop. Alternatively if you want to access music from multiple computers you could consider investing in a NAS drive so you don't need to leave a more power hungry computer on all day!
2: The 'People' hub in Windows 8 does allow for Twitter integration, however it's not really a 'full featured' twitter app. Best bet is to look toward the Windows store for your Twitter needs! I'd start by trying MetroTwit or Rowi
3: Don't fret too much about closing apps ... Windows does a great job of resource managing background apps, but to actually close an app, swipe from the very top of the screen all the way to the bottom and it will 'drag to close'.