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Make sure you are using crop rotation to help control any disease or fungus that is living in the soils.
I would recommend Neem Oil as is does work as both an insecticide and fungicide and does not hurt bees that you need for pollination.
Here are some links for you.

https://www.gardeningknowhow.com/edible/vegetables/zucchini/solutions-for-common-problems-growing-zucchini.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

If you are getting flowers but no fruit, really the only issue is pollination. Because of the high heat in much of the country this season, this can sometimes make pollinators a little lazier than they should be. Therefore, you may need to hand pollinate to make up for it. This article will help with that: https://www.gardeningknowhow.com/edible/vegetables/squash/pollinate-squash-by-hand.htm

Some common zucchini pests include cut worms, cucumber beetles, squash bugs, vine borers, spider mites, aphids and whiteflies. Most zucchini pests can be controlled with regular applications of insecticidal soap or organic pesticides like neem oil (which I prefer). Since these different pests can affect the zucchini plant at different times in the growing cycle, it is best to start a pest control regimen as soon as the zucchini plant is in the ground to avoid these pest problems on growing zucchini.

Here is more information on neem oil: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm

Yes, they are safe to eat. As long as the inside looks healthy, they should be fine. Just cook them as usual. Often this is caused by poor growing conditions or a virus (which humans cannot get). This article will help explain why this happens: https://www.gardeningknowhow.com/edible/vegetables/zucchini/bumps-on-zucchini.htm

Male flowers, which are non-fruiting, commonly drop off the plant and this is common early on. Once the plant begins bearing female blossoms, it is normal for them to drop off as well when the fruit begins to form.

Can you describe the discoloration or, better yet, provide a photo?

In the meantime, here is an article with information on the bacterial wilt that affects plants in the squash family:

https://www.gardeningknowhow.com/edible/vegetables/squash/signs-and-treatments-of-squash-wilt.htm

And, here's an article on common zucchini problems that may be of some assistance:
https://www.gardeningknowhow.com/edible/vegetables/zucchini/solutions-for-common-problems-growing-zucchini.htm

Happy gardening!