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This would be best applied in spring, as when the plants go dormant, they are not taking up nutrients as well as they would during the active growing season. It is very important to note that you should test your soil prior to application to ensure that the pH is below 7, as bone meal will not work at higher soil pH. You can lower this, most effectively with iron sulfate.

Here is an article that will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/bone-meal-fertilizer.htm

I would do this very sparingly, as sodium can be toxic to plants if used too often. Most of the time, neem oil is a better choice as this can solve many issues that sodium bicarbonate can be used for.

Here are two articles that will help:

https://www.gardeningknowhow.com/garden-how-to/info/baking-soda-on-plants.htm

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

Homemade fish emulsion can keep for about a year after it's fully fermented. Commercial products might have different shelf lives, which will probably be listed on the package.

You can, likely, source bone meal and kelp meal. Kelp meal will give you an organic source of potassium, while Bone meal will give you an organic source of phosphorus. These two should be used together, as they will both contribute to the flowering season. It would be best to supply these together.

Coffee grounds, contrary to popular believe, do not acidify plants or provide any special nutrients. It is best to add coffee grounds to your compost and use them this way. If you are trying to acidify your soil, there are products on the market that will give you better, and more consistent results. If you have leftover brewed coffee, you can water your plants with it (houseplants too) and this will add a touch of acidity. I would start with a soil test so you know what your soil pH is and if there are any nutritional deficiencies. A top-dressing of 2-3 inches of compost is often all that is needed for perennials and shrubs, roses being an exception. Look up [your state] Extension Service for soil test information.

To some degree, yes. I would dilute it down just a little before doing this. Tea is a good source of nitrogen, which is good for leaf growth, but it does seem to lack some nutrition for bloom growth.