October or November and around February is the best time
Clipping makes their coat dull so make sure to use a hot oil treatment after clipping.
All seasons. Just make sure that during the summer you don’t clip the whole body to avoid sun burning. If where you live it’s cold in the winter make sure they have adequate warm shelter or blankets.
Anytime you want to. Just make sure they are adequately blanketed in cooler weather to make up for the loss of heat.