[3.2] Self cast Lightning Tendrils+CwC+Arc CI Scion

I don't understand the transition from 61 to 71. You basically respec all those nodes once you get the witch start?

Yes. If you're connected to the Witch start and you took "Path of the Witch" Ascendancy, you can unlearn the path from Scion's ES nodes and unlearn Elemental Ocerload. And use those extra points to take the crit nodes around your tree.
You should do this, once you finished Uberlab (obviously) and bought yourself Choir of the Storm. You can take the lucky crit potion or crit chance gem on top of that. Basically, you should be able to crit at least twice per second to make full use of the Choir.
From this point, search for more crit chance/multiplier on your gear - high crit multiplier is a good way to scale into the late game.

So Choir is absolutely mandatory for this build?

It's not, but it adds quite a lot of single target damage.
Choir isn't mandatory, crits aren't mandatory, chaos conversion isn't mandatory, 6-link isn't mandatory. Those are "pieces" that further increase your damage to the point where you can actually do endgame content.
Without all those pieces, you should be "ok". Maybe you can still farm red maps, maybe only yellows. just do whatever content you can at the moment and farm for another piece.

I see your point. I'm only 22 now, lacking some damage but I'm sure I'll catch up soon when I have more support and damage nodes (damn those beasts with extra life+regen drive me crazy).

If you're having issues with strong single enemies, try pure Lightning Tendrils setup:
LT + Concentrated Effect + Controlled Destruction + Added Lightning Damage (or Faster Casting, Lightning Penetration - I'm not sure, what will give you more damage with your current gear).
You can get all those gems from vendors in town of from Siosa in Act 3 Libray.

for the bestiary league specifically, bringing a frost bomb if you can fit it in really helps vs the health regen beast's.

edit:
Question, what do you recomend as a chest peace before CI ? Incandescent heart's turning 25% of ele dmg recived to chaos dmg worries me.

I'm still confused about your Cast when Stunned setup. The Occultist node has "Cannot be stunned when you have Energy Shield"... and since you're going CI, not having ES means you're dead. Am I missing something? Would the CWS gem still trigger even if we can't be stunned?

You're right, I missed that change in ascendancy rework. I'll try to update it tomorrow. I guess, either cast shield and golem manually or use the CWDT setup.
It doesn't really matter that much tbh, the CWS+Golem+TS is least important part of this build, gives a little bit of defense and that's it.

Hey man, loving the build so far! Just wondering though, why do you unspec the Static Blows cluster, the one before Eldritch Battery? Is the dmg and shock chance just better spent on crit etc? Thanks again