Hi Swisser,
Firstly, please have the camera try level every time you start the gimbal. While the LED is flashing orange, it is sampling which way gravity is and the accelerometer uses this to keep itself level. When it activates several seconds later, it will use the sample it gathered while calibrating. If the gimbal was moved while it was calibrating, it will have a slow drift.
To answer the rest:
1. You can connect the BEC into the Pan Input lead on the Skyline. OR you can connect the BEC to your receiver and then the receiver will power the Skyline.
2. Please connect the "Tilt Input" to you receiver. Elevator or any other channel that can be controlled with a slider or stick on your mechanism (and returns to neutral) should do.
3. The roll is stabilised by the Skyline. Once set, it does not need any input and can be left unconnected. The roll input will be re-enabled on the next firmware.
To use the Set Level feature, do this:
I. Adjust the slider gains so that the gimbal doesn't oscillate.
II. Press the "Power On" button.
III. Using the up & down arrow, adjust the Roll Centre Tune value until the tray is flat.
IV. Press "Set Level" button.
V. Untick the "Power On" button (the servos will deactivate and probably roll if the weight is unbalanced).
VI. Press "Save Settings"
VII. Disconnect the battery and USB cord.
The level should now be set. If done correctly, it should hold its value and when you power it up. For slow creeps, check your radio to make sure it is trimmed.