XD, YD, and ZD usually mean the difference in X, Y, and Z that the particles can appear in from the coordinates that you gave. This means that rather than all being summoned at an exact point, the particles can cover an area.

For example, /particle smoke ~ ~ ~ 10 0 0 0 100 will create a long line of particles along the X axis. /particle smoke ~ ~ ~ 1 1 1 0 100 will create a small box.

This does not affect the movement of individual particles though, you most likely want the <speed> argument. If you make this 0, the particles should not move as much. Keep in mind though that many particles inherently have some small movement that is unavoidable.

Nope, that's totally correct.

What you're seeing is the damageIndicator particles. It is used when a mob is damaged by a strike (when you've timed your attack correctly, as opposed to spam-click post-1.10).
You may be confused because they are indeed very similar to the breeding particle, only darker (in terms of when using the default resource pack).

See http://minecraft.gamepedia.com/Particles for a list of particles in the game.