No. A sacrifice is when the batter turns around to bunt and lets everyone on the defense know what they are going to do. The batter is 'sacrificing' (allowing the defense to get him/her out) so the runners can advance one base.
It is a base hit once the batter-baserunner passes first base. This will not change by being thrown out at second.
Nope, when the batter is hit it is a dead ball.
That would depend on how the runner was retired at second base. For example, if the runner slipped and fell on his way to second base and the outfielder had the time to throw him out on a force play, the batter would not get credited with a base hit. If the runner made it to second base safely and then slipped rounding the bag and the outfielder threw to second base and the runner was tagged out, the batter would be credited with a base hit. If a runner is forced out at any base, regardless of where the ball was hit, the batter is not credited with a base hit.
If the runner at second is out by being forced out, the batter is not given a base hit .... the play is ruled the same as if the ball was hit to an infielder that threw to second to force the runner. If the runner at second is out by being tagged because they rounded the base too far, the batter is given a base hit.
A double is when the batter reaches second base on a hit ball.
If he tries to stretch a single into a double and is thrown out as a result, then no, it is scored as an out at second base, not a base hit. The above is incorrect. The batter would be credited with a base hit -- specifically, a single -- and also as being thrown out at second. Check the box score from the Phillies night game of 2012 September 9 -- in the fifth inning Ryan Howard was thrown out at second exactly as described as above, but was credited with a hit.
he could have made a balk ... walked the batter or hit him with the ball ...