Cloak of Defiance + Bloodseeker Build (help please)

I haven't asked for build help here before, so apologies if I do something wrong (for instance, I'm not even 100% sure I want a scion base, but it seems like an ok start point, so I've put it here).

Ok so basically I've played some very high DPS characters before and now I want to try something that, at least in my head, seems like very high sustain. The idea is using Cloak of Defiance and bloodseeker combo, having instant leech for life and percentage based leech for mana, while of course taking 40% of dmg from mana up front. Of course Eldritch Battery will be part of the mix to buff mana pool and because energy shield seems like a hindrance when using mind over matter anyway.

I'm here though because besides the framework of the build, I'm not really sure where to go and have a number of questions I could use help with.

1) Which attack(s) should I use? Dual Strike seems obvious because Bloodseeker isn't the highest dmg weapon, so I could put something with higher DPS in the off hand while still getting the instant leech from bloodseeker. Other good options I should be thinking of?

2) How should I prioritize things when building my passive tree? It seems like this is a complex character in the sense that it wants life, mana, mana regen, and even ES is good as it will ultimately be converted to mana. The complexity though comes when I start to think about effective health, or how much damage it a character can take before dying. Basically with no mana regen a character who takes 40% of damage from mana before life would be best served by having a mana pool equal to 66% of life. For example 1500 life and 1000 mana would result in both pools being depleted at an equal rate until death, so that there wouldn't be extra mana left over, but neither would mana run out before health.

Once mana regen is added into the mix though, this seems to change a lot. It seems like it becomes a function of how long it takes for a character's life to be depleted and then factoring in how much mana is regenerated over than time, rather than looking at the actual size of the mana pool. So in the example above, it would take 10 seconds for the character to take 2500 total damage, it doesn't really matter how big the mana pool is (well it needs to be big enough that it holds at least 40% of the damage of a given hit at any time), but rather that said character regenerates at least 1000 mana over that period of time. Am I looking at this the right way? Is it all just a crapshoot given life pool will basically always be full thx to leech, so just maintain enough mana and regen to always be absorbing 40% of incoming dmg?

Maybe the most productive way to think of it is based on what content I plan to do and what incoming dmg I can expect from it. Spike dmg is certainly the most dangerous, so maybe I say in certain cases I may want to tank something that can hit me for 4k dmg. In that case ideally I'd want a) 1600 mana available to soak dmg and b) ability to regenerate that mana quickly enough to eat follow on attacks. Yes/no?

3) What other defenses should a character like this focus on? Maybe even try for something like Iron reflexes? I'm assuming acrobatics would reduce energy shield before it gets converted into mana, which wouldn't be good, but is that correct?

4) Back to the forum identity issue, is scion the right place to start?

5) Other unique gear I should look for with this build? Right now, sticking with the suitability theme, I plan to run stun immune and maybe freeze immune as well. Oh and I can run a shav's ring in the slot to help with mana regen if that matters.

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I'm sure there are other things I'm missing, but if I can get some help with the above questions to start, it would be a great help. Thanks in advance!