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Yes, as far as I know this fertilizer is good for just about any plant, including edibles, and safe to use. As with any fertilizer product, be sure to follow label instructions carefully to obtain the greatest results.

Lowering the pH for the nutrient mix would be the only way you would have of lowering pH for your plants, since you can't change the pH of your mix. I would suggest you might consult with the maker of your flower enhancer to see what kind of research they have that might better answer your question.

Yes, they are very good for the garden. This article will have more information on coffee grounds:
https://www.gardeningknowhow.com/composting/ingredients/coffee-grounds-gardening.htm

Eggshells are beneficial because they add calcium, which is particularly good in vegetable gardens, as it helps to prevent blossom end rot. You do not need to break them up, but they will compost faster if they are broken up. You can also compost them. Here is more info: https://www.gardeningknowhow.com/composting/ingredients/eggshells-in-the-garden.htm

Compost and composted manure are always good. Beyond that, I would have your soil tested at your local extension service. This will tell you what the soil needs and then you can determine what additives you need to fill that need.

Nutrient amounts are technically figured in pounds. If you're trying to figure out how much fertilizer to apply to a given area, you need to consider the size of the area, the concentration of the fertilizer, and the type of plants. I might add that determining lbs per acre, or even sq ft, is usually more important in agriculture than home gardening. Most people just use fertilizer as recommended on package, sprinkling or pouring around each plant. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-npk.htm

Sand is usually used for drainage. This sounds like a recipe for potting mix or planting soil rather than fertilizer. It's impossible to comment on the proportions without knowing more about the composition of the "soil" component, and the condition of the cow dung, i.e whether it is fresh, dried, or composted.