Can the umpire call a ball without a pitch being thrown?

Answer 1

No, the umpire can't call a strike or a ball until a pitch is thrown. There is no other play that uses those calls. An umpire can, however, walk the batter without a pitch being thrown if the pitcher attacks him. He can also advance a runner without a pitch being thrown if the pitcher balks.

An umpire can, indeed, call a "ball" prior to a pitch. This is part of the rule designed to prevent the "spitball." This is very specifically spelled out in MLB Rule 8.02a. The pitcher may not touch his hand to his mouth while inside the mound, apply any substance to the ball, deface the ball, spit on the ball or his hand, or rub the ball against anything. The penalty is that a ball is called.

Answer 2

They do if it is close or borderline to a strike

Answer 3

Yes. If a batter refuses to enter the batter's box, he is out. A batter is also out if someone else already in the lineup bats in their spot.