Congratulations on your new MBP, outstanding device.
-To migrate your content from your PC to your Mac you have different options:
1- You can use home sharing, but if it's too slow or messy then
2- Use an external hard drive or usb flash or
3- Download Box, Google Drive, Dropbox desktop app (or whatever cloud service of your choice) into your PC, move all your stuff there ---> Download desktop app in your Mac --> download all your stuff here. That's it, easy peasy.
- To backup your iPhone (and download your content) in your new Mac you need to do a couple of things:
1- You need to authorize your iTunes in your Mac.
Plug your iPhone > open iTunes > go to "Store" in the menu bar > Authorize this computer
2- Right click your iPhone in the list (on iTunes) choose back up and/or transfer purchases.
Keep in mind that it will back up your settings, apps etc but not the music, if you try to sync your iPhone (and its music) with your new Mac BUT the music is not in your Mac, chances are it will be erased on your iPhone. As far as I know, you cant back up the music you didnt purchase in the iTunes store back to your mac, you have to do that manually.
To Transfer your music from your PC to your Mac, you can use different methods, the one I used was: I transferred the whole iTunes media folder from my PC > external hard drive > Dragged into iTunes on my Mac (of course I set up iTunes to automatically keep my music folder organized).
I hope this helps.