Help understanding servo control loop


I am looking at buying the following development boards for a zed board controls effort.

It looks great, but I need some help with the general system architecture to better understand what I'm in for.  I need to control a voice coil accurately and I'm consistently being sent to the "servo control loop" topology.  I've attached an example block diagram.  

To some degree this makes sense.  My voice coil will have a load attached and go where the "DC Servo Motor" block is shown. I also have velocity and acceleration maximum specs.Some of my questions are the following:

1. Why isn't regulation done solely with the encoder?

2. What is the purpose of the current feedback?

3. Does the current feedback provide acceleration information?

4. Do I need to use a force/motor equation to related current to acceleration?  This wouldn't be bad in theory since it could be a straightforward calculation if so.  

4. Is there a conversion required to go from position (x value or displacement) to velocity (x/t) to acceleration (x/t^2)?

I'm a little new to this so I'm trying to get my head wrapped around this approach.  Thanks for any feedback!