Hi,
you need to handle the add / remove actions by app controller. For each add you need to draw a new instance ID, so that FPM forces a new from instance. Then GET_DEFINITION and GET_DEFAULT_CONFIG gets called (once for each add, but this suffices). In GET_DEFINITION you build the field catalog for name value with correct type. In GET_DEFAULT_CONFIG you place the label value pair on the UI. The rest is standard.
Regards, Jens