The finches will mostly keep their base color and eventually add in more mature feathers that may show their gender. The last picture looks like a fawn or recessive silver zebra finch, or it might be a regular gray, though it's kind of hard to tell with the picture.
Here's a good site for...
I usually hand raise my zebra finch babies, so I'm not sure about that question. I think handling them at a younger age will help get them more used to humans. Although, they probably won't get as tame as hand raised finches, but may trust you enough to perch on your hand.
Well you can't really stop a finch from breeding unless you remove one of them. You could try to use fake eggs the next time they decide to hatch a clutch, or just shake up the eggs they have laid and set them back in the nest. They should eventually get the idea that the eggs won't hatch and...