No, Etsy automatically puts your categories and attributes as tags already. You don’t need to repeat them and waste the valuable 13 tag space.
No, whether it’s plural or not count as the same thing. “Dress” and “dresses” are the same to Etsy.
Technically this shouldn’t affect your ranking of items, but it limits the keywords that you can rank for, leading to potentially lower views and sales. So mix up the keywords and use different ones if you can.
Although recency is one of the ranking factors, the effect is very short-term. Usually it only last for a few hours for more popular search terms. And the boost in ranking seems to be small. Because the $0.2 can add up over time, I wouldn’t recommend renewing regularly.
Although listing video is not a ranking factor, an informative video can improve shopper experience. Your video can showcase how your product works, how it looks in motion, and how it can be paired with other products, etc.
It can make the product more desirable and making shoppers more likely to buy. Therefore increasing the search ranking.
Similar to the listing video reasoning, number of images itself doesn’t affect ranking. But more images can help you showcase different aspects of the product. And that can improve conversion rate and ranking.