M4/3 vs APS-C

In theory yes, if you think of resolution and high ISO performance. But in practice it doesn't seem so when comparing the existing top models. It is not only the sensor size that matters, it is also how the camera handles the output from the sensor. And there Olympus at the moment seems to have an advantage before Sony. But this can change of course.

Regarding depth of focus it is up to your personal taste. If you want deep focus, m4/3 is better, if you want more shallow focus, APS-C is slightly better. But still not like FF.

The big advantage with m4/3 is the size. Especially of the lenses. That's the main reason for me to choose OMD before NEX7. But I really like both cameras, so I'm not quite sure I made the right decision. But I think so.