OS X, Parallels, and Windows (8)

So I'm thinking about getting a MacBook as my next laptop. It's been over 7 years since I've last regularly used a Mac, and thus I've become rather entrenched in Microsoft's ecosystem. I don't plan to give up Windows anytime soon, so I'm planning to use something like Parallels to help augment Boot Camp when I'm in OS X. I had a few questions so I was hoping that someone out there is familiar enough to know the answers.

First, how bad is the performance hit when I'm running a Windows program virtualized? Is it noticeable? I don't plan on running anything too intensive virtualized. I'd reboot into Windows if it's something intensive like gaming. I suppose the program that I'd be using the most virtualized would be Office (unless the Mac version is indeed as good as the Windows version).

Second, how does file sharing across the two partitions work out. From what I understand OS X can read the NTFS Windows partition, but it doesn't write to it. And it sounds like Windows doesn't read or write to Mac partition. Does Parallels help this situation at all? Or am I still going to have to have two copies of each file, one per partition? Even if Parallels doesn't help this situation, does anyone have any advice on how to handle working on a given file between the two OSes?

Does anyone know how well Windows 8 Metro/Modern apps work in Parallels? The reason why I'm asking is because I have an active Xbox Music subscription that I'd like to keep using even in OS X. The only way to do so would be through the Xbox Music app though.

Thanks in advance for any info!