>Can you disassociate the focusing from the shutter button on >the D3200 and use a back button for focusing instead?
Sure. Go to Setup>Buttons>Assign AE-L/AF-L button. Choose AF-ON. When you do that, AF is activated when you press the AE-L/AF-L button *only*, and pressing the shutter release no longer triggers autofocus.
If you've downloaded the D3200 manual, it's at the bottom of page 143.