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Wood ash can be used in the garden, but you should read the articles below to properly implement them into the soil.

https://www.gardeningknowhow.com/composting/ingredients/composting-ashes.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/using-wood-ashes.htm

If you can include a picture then it will be very helpful. It almost sounds like you are describing a mantis, which are very beneficial to plants.

I see. I can't tell what it is. It does not look harmful to plants. In fact, it looks like a predator. Unless they are doing damage to the plants, I would leave them. They might be doing you a favor by eating other bad insects.

Yes, drought will have an effect of flowering, the tree likely needed to save energy and did not produce flowers.

Check with your local County Extension Office to see if others are reporting lack of flowers in your region.
Here is a link to help you locate your nearest office.

https://www.gardeningknowhow.com/extension-search/

I believe that this article will answer your questions: https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-pruning.htm

If you can send a picture I will be able to help better. You can check to see if it is alive by breaking the very tip off of a branch. If it is brittle and has nothing holding it on, or is not green inside, then that portion is dead. You will want to take off everything that is dead until you reach living tissue. This will let you know if your tree is still alive.