Most are not. Some people don't like small, fast, rodent-type animals.
Yes. While their food mostly consists of seed and vegetable crunchies, a gerbil would also be happy chasing down a cricket or mouthing a mealworm. These add protein to your gerbils diet, which is especially great for pregnant or nursing moms or young gerbils!
Cats, birds and gerbils aren't typically afraid of the dark, but animals have their own personalities, therefore, any one of them can be afraid of the dark. The best way to make them less afraid is conditioning them with positive reinforcement.
Other gerbils.
Gerbils are an animal and can not be "invented".
Male gerbils can be neutered, but it is not recomended. Female gerbils should not be spayed. In general male gerbils should not be neutered unless there is a good reason for it.
no gerbils are not originally from the UK but instead from the deserts of Asia. But you can still buy gerbils in the UK
Yes, mice are smaller than gerbils, but I think gerbils are the right size.
They do have seizures (this is common in young gerbils)
No, they are not related. Gerbils are rodents, Rabbits are not.
No, Gerbils are vegetarian.
Gerbils and nothing else.
Yes, e.g Mongolian Gerbils.