The PlayMakerFixedUpdate script is automatically added if your FSM needs FixedUpdate events (e.g., one of the actions you use needs it). Normally it's hidden, but in some situations it ends up visible, I'm still tracking down when this happens. You can safely delete it if you want.
Normally you access Plugin Import Settings by selecting a dll in your project. There are different dlls for different platforms. There is a dll for WP8 for example. You shouldn't need to change these settings...