I am happy to tell that after about a month now I kind of getting it now with MB.

what I can advice to any noobie like me is paying attention on how to use the layer and switching between IK and FK. it turned out that I have to best and most predictable results when plotting VERY often. now I usually key on 1 layer above the base at the most. as son as I am happy with what I can get with this one layer I plot the keys immediately onto the skeleton as a kind of backup and go back to the empty layer. this prevents the rig from goin crazy when I have to key IK and FK on more than 1 layer. I can´t exactly tell - it´s still all intuitive by now, but I had some issues when keying different layers, switching between IK and FK. every time I dragged the from IK to FK or back the skeleton shifted in movement. so after some while it becomes (at least to me) way too complicated keying in the right mode and not getting lost in making corrections to my own added on-top-animation.

whatsoever - MB turned out to be real fast compared to Maya with animation stuff - now look at me, who would have guessed that..? I just had to get my brain cleaned from maya workflow and wrap it around MB.

thx to all of your helps!