A front camera alone are just fine, if nothing else it will capture what you do with your vehicle, and if you follow the code as set forth by the wizz kids we elect to govern us, then at least whatever happen cant be your fault.
And i do personally think the cases where the wrong part get to pay for something are often based on claims that single camera can refute.
It is only when you get into pointing fingers at people in traffic more cameras become a good thing to have, and still pretty much all the things i have filmed in the past 8 years have been captured by my front camera.