I'm still working on my Jump 'n' Run and have already solved the "can I jump" question.
My Question is now, how should I configure the Gravity, the Timesteps, the Fixturesize, the applied Impulse and the Fixturedensity for the most realistic result?.
The Fixturesize is now at 230x140 and can't be changed cause I need the pixelexact size for debugging. What can be changed is:
Gravity(10),
Timesteps(Deltatime*4);
applied Impulse(1000000);
Fixturedensity(0,002);
And why do I need an Impulse of 1 (!) million to move a current mass of 65kg?
Please do not use pixelexact sizes, this will make the engine perform and act poorly. It's in mks (meters-kilograms-seconds). A 230x140 meter object is a little large. Also object speed is capped at around 200 m/s, so you won't get that moving very fast. If you need help with transforming, take a look at the OOBViewportTransform class, which is provided in the common package.
The impulse and density only matter in relation to other objects. So you might want to create a level first, and then test how your character interacts. Starting with densities of 1 is usually fine. You generally don't want to make either too high.