Z-homing adjusted, now it homes down, and moves up afterwards. IN homeall.g Z is first homed, then the other axes.
solved a lot: basic configuration, virtual endstops, direction of Y axis, homing directions. as it is right now, the machine seems to home correctly. There may be a bug in the firmware that ignores the axis value for a given G28 command. instead the values from M208 (set axis max travel) are used.