I'll go along the points you've noted in the screenshot.
A. Try using the Intelligent labels of the RadChart. You can do so by setting the IntelligentLabelsEnabled property to true:
You can also check out this demo
to find out more about the feature.
B. and C.: Depending on how your business classes are structured, you can see if using Empty Values
will fit these requirements. I have attached a simple project to demonstrate the empty values functionality of the RadChart.
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