Hand drag and drop with body hanging on it

Hi there.
After two days of struggling, two unhelpful unity-answer-questions and some dozen tutors, docs and older threads I was going through, I think it's time to set up a new thread about it.

The thing is, I want to learn that stuff; 90% I can get by try&error, but now I'm stuck. Unity docs seems to be very weak by more specific work, and it seems there is no other thread like that before.

What I want to do: make my character able to climb with single controlled limb placing.

What I've done until now: I took the FPS prefab bevause its simple to work with in the first attempt.
I've a testlevel good enough to work with. I've made arms with armatures in blender an imported it to unity.
I've made a script to detect edges and convex surfaces at any object in the world. I can place objects like the bones of my characters hand on those edges and surfaces and let him 'grab' it, controlled by mousebased drag and drop.

What I need to do: The limbs should work like a chain, one end attached to the FPS-Rigidbody, the other end to the hand placed on an edge.

My idea: Link the bones together by joints, that the entire arm is following the hand that is groping for an surface to grab. This works just in the climbing mode, you can toggle in (that works). Then, add the FPS-Rigidbody to a replacer-empty to simulate 'hanging'. Some other actions like climbing higher by placing the limbs higher at the wall should be possible.

My problems: First: the bones wont connect correctly. I did it with every joint type now, did the unity-joint-tutor step-by-step. My bones are just wobbeling around somewhere in the worldspace, even with or without kinematic rigidbody; I've tried to tweak every value up an down... nothing seems to work.
Second Problem: I'm a completely newbie to animation in unity. I work since over 10 years with blender and I know rigging and animating and use it there since years successful. In unity I can't manage to make that skinned-mesh following the bones. After import, I've configured the skin with the correct bones, but it doesn't work. Here the answer-question about it: >> Link <<

Every help is welcome! Greetings, Ambrose

 

It seems there is still no possibility to set up some near-realistic joints.
After a lot of error&error trying, the joints are almost joints now.
Is there any way to make them more joint like and less bubble-gum like? All movement is already locked.
I can make them stick more by increasing the rigidbodies mass:

But they wont move that way. Otherwise I can lower their mass to make them more movable, ...

... but makes them bubble-gum stretchy again.

So, why can a joint not be a joint in unity??

 

Well, I've got it: the joints have nothing to do how the hold-together connection really works. The rigidbodies are important.
What a mess. Nobody knew that I guess.

At least, has anybody a clue how I could connect the body to the player, the player to the arm and the arm to the hand without a force feedback that mess up everything?