1. Umm, the SP is a seperate entity. If you have a fire navi with a water SP and you use a lava stage change, the SP will be dmgd by the lava. HOWEVER, SPs can be upgraded to have terrain immunity relatively easily, so this is not much of an issue.
2. From my understanding, it works something like this:
IF dmg > than the health of the barrier
Dmg dealt= dmg done - barrier's health
If there is break/impact involved
dmg dealt= dmg done - barrier's health/2
So, with examples.
50 hp barrier gets dmg for 30 (30-50=-20) -> 20 hp barrier left.
50 hp barrier gets dmg for 60 (60-50=10) -> 10 dmg dealt.
50 hp barrier gets dmg for 30 and break (30-50/2=5) -> 5 dmg dealt
since break/impact only doubles the effectiveness of the attack against defenses, you'd have to double the dmg, deduct the barrier, then half the dmg back. it's easier to just half the barrier's value
3. Alright, you get why someone would use free action busters, right? 30 points for 50 dmg is awesome, even though you need to upgrade your buster to max for it. Now, the problem with this is that it doesn't carry any effects. It cannot be used to break, or have any element, or base barrier HP on it, or anything like that. Buster base is weaker point by point, but it lets you modify the "type" of the dmg.
4. Flexibility. With clever use of terrain and sigs, you can always have an elemental advantage. I do admit, they feel a bit underpowered, but not overly so.
5. I think that's actually effect rage and effect skill, both of which are crossed out right now DX
6. Folder crash can only be stopped by the crash counters, silence can be removed by status curing effects. Crash can also ruin your systems for good.
7. Yes.