#2 What is the warranty? How long is the warranty? Is it a full warranty or a lesser "limited" warranty?
1 Year Whole unit(include Parts and Labor),3 Years on Refrigeration System(Include Parts and Labor),5 Years on Compressor,
#3 How often should the unit go into defrost mode when the unit out operating in 60-65F temps? Mine seems to defrost pretty frequently.
It goes to defrost mode more often if the room temperature is below 60F.
#4 Do you need to purchase the controller, or will the unit work without it?
The unit will still work without the controller.
#5 Can the HD90 be hung from a joist or center beam by using the unit's top handles?
It is not safe to just use the handle to hang it. The handle is used to carry the unit around but not for hanging. You can use a hanging kit that will support the unit from below.