Good questions and there will be many different answers I'm sure...
Prior to takeoff:
If the aircraft's surfaces are contaminated (except for flaps because they were retracted at the time) but there is no more precipitation falling, then I would de-ice with Type I and leave the slat/flaps in the retracted position.
If the precipitation is still falling then after Type I, I would request Type IV anti icing fluid and I would set the slat/flap setting to my takeoff configuration of that day. Once anti iced and prior to taxi I would retract the slat/flaps to avoid contamination while taxiing.
After landing:
If I suspected moderate to heavy icing, I would not retract the slat/flaps fully until a visual inspection was accomplished. In any case if you were to do a turnaround they would have to be selected down to de-ice them.