1) How come High Elf Reavers don't get to shoot 360 degrees like Pistoliers and Kislev Horse Archers?
The rule thing: normally units that shoot to the front has 30cm, that is the case of Reavers. Units that can shoot 360 usually has a range of 15cm. That is not always true, the best way is reading the description of each unit.
The fluff thing: as I see is that Reavers are disciplinate archers that can shoot raiding. The sense of the unit is having archer raiders that can shoot as a block following orders, so they shoot to the front. While pistoliers or Kislev Horse archers are a group of raiders, that act as a band shooting in any direction following the intuition or war expirience of each memeber, so they can shoot in any direction but the lack of organize fire makes them only effective in close combat.
2) Is the High Elf army always hitting on 3s for shooting so powerful - that the Tournament ruleset is always preferable?
In my opinion if one player is rookie and confront a veteran is preferible that the rookie has the basic list. Tournament list is more balance with other lists.
3) When I charge, do I get to change formation before I contact enemy troops?
Yes and this is important.
- Take the stand closest to enemy.
- Move center to center to the closest enemy unit stand (target enemy unit).
Then move the second stand of the attacking unit expanding the battle line. It means to a place touching your - first stand maximiztion the front to enemy unit.
- Then do the same third stand.
A stand can not move more than his movement. If the stand can not touch the enemy because this and they can place supporting the stands of its own unit that are fighting.
(The rule set explain it better than me... for sure)
Remember that a unit in irregular formation moves at half path, but can move full path if he is charging to enemy.
4) If it is my turn, and I lose a combat to an opponent, does he get to advance into more of my units to attack them, even though it is my turn?
Yes, if you attack in your turn and loose the combat, the winner could claim its right to make one advance. To 20cm if he make the breakthrough (destruction of the unit in one dice roll) or 10cm if he destroy the unit in subsequent pursuits.
5) Can I move the same distances backward as I can going forward with a unit? It seems that I can rotate my units any way I wish rather than in Warhammer which is very strict about facings.
Yes, infantry moves 20cm and orientation of the stand did not consume movement. Notice that the orientation is the stand not the whole unit. Each stand can not exceed the movement. 20cm in regular formation / 10 in irregular formation.
When the combat phase ends, all the units
that had been fighting, are allowed to rearrange its orientation in the following way: Choose a stand of the unit. Change its orientation, then arrange the other two stands touching the stand that has changed its orientation.