1. On parented cameras (face, hand, posing, and any orbit camera set to "orbit selected") on the camera's Properties put a check next to "Limit Orbit to 360" This should stop cameras from flipping upside down.
2. I suspect you are bending a body part in the middle of an active IK chain. For example bending a thigh when the IK is on for that foot. Try Turning off IK for the limb you are editing.
3. Selecting any body part should have no affect on the library. If selecting a body part is changing the library view please file a report with support. I've never seen this actually happen. Please include exact steps to make this happen.

If your scene is slow when posing try setting your preview mode to "Smooth Shaded"