I would collect, wash, harvest, and reuse a portion of the yeast only. You want to keep the yeast generations as low as possible. Resusing the same cake over and over again will lead to off flavours as the yeast get old and start to die off. It's better to use part of the cake and let them regrow into new yeasties, but if you save the majority of the yeast cake from the first batch and split it into 2-3 portions you can use one per batch of new cider. General rule of thumb is to not go past 5 generations with a culture, and definitely don't reuse the same cake multiple times (I wouldn't reuse a whole cake even once).