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Cucumbers grown for pickling will yield the best product. The skin is less bitter than slicing cucumbers and they have smaller and fewer seeds.
European Cucumbers are used frequently for pickling.

It appears that the yellowing is caused by a lack of nitrogen. Apply a nitrogen-rich fertilizer to fix the yellow leaves. Under-watering will appear as wilted leaves, and over-watering will often cause rotting, and brown or black spots. This article will help: https://www.gardeningknowhow.com/edible/vegetables/cucumber/tips-for-growing-cucumbers.htm

It has definitely undergone some nutrient change, but this is not harmful. This is natural for it to turn yellow once it is over-mature. They are still safe to eat, but the seeds will be fully mature, and no longer soft. You could still use the cucumber but save the seeds for planting.

Here is an article for more information: https://www.gardeningknowhow.com/edible/vegetables/cucumber/when-to-pick-a-cucumber-how-to-prevent-yellow-cucumbers.htm

Tomatoes and cukes do not like cool overnight temps. Wait until night-time temps are over 50 and daytime temps are at least 70. These crops love hot weather. So go by weather and not dates although you can easily search for your frost-free date(there are three college stations in the US). Wait about 2 weeks after that date to put out cukes and toms. Green beans are best grown from seed planted outdoors after your frost-free date. They germinate and get established rapidly. Transplanting slows them down.

I am inclined to believe that this is a fungal infection, likely brought on by a pest. The best thing I could recommend is reconditioning your soil with dolomitic lime, and wettable sulfur during the off season. This will kill most infections within the soil, as well as correct very common cucumber deficiencies.