Adding Poles and welding an arm to the Torso (Inverse [IK])

Hello Devs,
Ive ran into this problem to many times now. I am using Inverse Kinematics in order to move a Part realistically. My question is how to add a Pole (hidden instance which is only accessible via script) in order one joint is in the right direction. Secondly, I wanted to know how I would be able to kind of “weld” this part:

to the torso. The Torso will later move and this is how it looks for now:

(the arm doesn’t move with torso + poles don’t exist so the joints don’t stay out, they move in and out)
I already tried it with every possible constraint/weld/etc. and it did indeed work, only that now the UpperArm ( nearest part to the torso ) is now sticking with the torso, only that it does not move with the other arm-parts anymore… I want to recreate this effect:

(you can clearly see how the pole of the upper and lower arm stays on the outer side + how the arm moves with the torso)
in an effective and clean way, however didn’t find any good ways to solve my problems.
Any help is appreciated, thank you!

PS: with Pole I mean that the joint should stay on one point. As you can see here, the joint between the upper- and lower arm-part is sometimes positioned down, sometimes up: