On one hand things are going great and i'm learning a lot on the way.
On the other hand i realized that reading the Position of a servo, like it is shown in the Arduino example-code of the Motion Kit, is not sufficient as sensory-data (it just represents the applied position/velocity). Due to physical interaction i want to track the real, measured angle to compare with the desired.
So in the long run i'll use servos with Position-Feedback to read the angle from the additional wire. As noob its hard to compare any specs, but the "KST MR320 PF" may be appropriate as replacement (still confused about the min and max angle it can take, it must not turn infinite, but a range of at least 270° would be great).
For the current prototyping, i will extend each servo with an Angle-Module (potentiometer), combined with a PbHub and connected to the Motion-Kit. This may be a bit overkill (in cables and weight), but cheaper and sufficient to have a nervous-system as processing-inputs.