MicroG is an implementation of gapps, or a collection of Google-provided applications, frameworks, and services. Without it, it will be hard to run apps that depend on that support (most apps present in the Play Store); even if an APK of that app is downloaded it will not be able to work properly.
A free-as-in-freedom re-implementation of Googleβs proprietary Android user space apps and libraries.
I find personally that my current distro takes up barely any space compared to Windows and a few games only, so there's minimal overhead to having two operating systems on the same disk. On my current setup I have a single SSD dualbooting both operating systems; Windows is ~ 180 GB while my daily driver distro is a 20 GB partition, of which it currently takes up 10 GB of space. There's not going to be a lot of overlap in applications that you install on both systems, and it even helps you develop better habits. No more gaming when there's work to be done; you have to restart and boot into Windows to do that π
Another thing to consider is that for all of the distros I've tried (not a lot), you can easily access files stored on your NTFS Windows partition. You can just mount it and access files there when you need them.