1. Yes. Sirens call goes away at the end of the creature's action phase rather than at the end of the round. So if you use it during final quick cast, the creature's next action phase will be next round.
2. It will be 6 dice. The Water Elemental loses the first melee +1 bonus, which it couldn't have utilized a second time anyways, and gains a new melee +1 bonus. The second attack is the first attack made with this new melee +1 bonus, so it gets to use it.
3. Short answer: Yes. It would get another sweeping attack without having to pay another 3 mana. I'm not going to give my longer answer unless people express interest, because this is actually something I have a problem with.
4. Absolutely! Akiro's favor doesn't stop working just because you're targeting yourself. Just like Bear Strength wouldn't stop working.
5. If the Pillar places a Burn on the creature, then the Burn HAS to be resolved this upkeep phase. However, your opponent gets to decide the timing of the Burn regardless of who's initiative it is. Cause it's their creature that's burning. So, if you have initiative, you might choose to attack him before he regenerates, but if you fail to kill him he can then choose to regenerate before resolving the burn.
6. He definitely gets the -1 discount when binding a different spell to the wand, so he can do so for 2 mana instead of 3. Also the FM can definitely steal the wand and use it, but I'm actually unsure if the Rune would work or not. I can't find this covered explicitly anyplace. I would personally apply the same logic as for the Beastmaster's Pet or the Priest's Holy Avenger. For those, the ruling is that even when you take control of the creature, you don't take control of the ability marker. Meaning that the ability marker still works, but it continues to reference it's controlling Mage whenever you read the text for it. For example, if you Mind Control a Holy Avenger, it continues to have Life +5, but it only gains the Melee +2 and Piercing +1 if it's target had attacked a creature/conjuration friendly to the Priest. Making it much less useful for the Forcemaster.
With that logic, because the Rune says "you" may pay 1 less mana, and "you" continues to reference the Warlord, it would not be possible for the Forcemaster to get the discount. She could benefit from stealing the Rune of Fortification or Precision though.