Is a small amount of water sufficient to wash a limb, such that some water drips from part of the hand and the rest of the hand becomes wet, or must the water be plentiful, within the context of "if water is flowing over the body, and you move your fingers over it with the flow of the water, and the water is present on the very limb over which the hand has passed, then this is a valid washing"?

What matters in ghusl (definition) (ritual bath) is the flow of water over the entire limb, not the quantity of water, whether abundant or scarce. So, if water flows over the limb, it is sufficient. It is not a condition for water to drip off the limb; rather, the condition is its flow over it. It is sufficient to spread the water with the hand over the rest of the limb if it has been poured on only a part of it.