I'm not sure about number 1.
Regarding No2. I wouldn't suggest it.
Your comp does have enough "Hour" soakers in DPS to do it, but... The biggest issue I see with this fight is making people, especially frustrated raid leaders, understand 3 healing is not better. We haven't seen many of these DPS race, hard enrage encounters in recent tiers so lets take a look at why it is a bad idea.
As shadow lets assume you do 30k on this fight. The Blue Buff pops at the 210 sec mark. So you will have done 6,300,000 damage to the boss at that point. Lets assume as a Holy Fire/Smiter you do 15k during the same period. So you will have done 3,150,000 damage at the 3.5 min mark when you switch to PoH spam. As shadow your DPS continues until the 5:15 mark, like you did with two healing. That is another 105 sec which is @30k is 3,150,000 damage. So at the wipe point of 5:15min as shadow you would have done 9,450,000 damage. At the same wipe point as Disc you would have done 3,150,000 damage, which leaves a "hole" of 6,300,000 plus the 7% you couldn't get before you have to make up with your leet heals. If you could keep everyone alive until the 6min Hard Enrage you might be able to pull it off. Unfortunately the effective enrage on Heroic mode is right around 5:30min mark. After that you just can't keep up with the incoming damage.
7% life at 5:15min means you are doing it right, you just need to do a bit more each to make it happen. Moar Deeps pls!
Good luck btw, its a brutal fight.