Are benign cardiac arrhythmia's anything to worry about if they only happen every 2 years?

Not likely. Without knowing the "benign" arrhythmia and other aspects of your health, I cannot accurately answer your question with any greater certainty.
Depends. By definition a "benign" arrhythmia is an arrhythmia that does not pose a danger to the patient's health; so if a cardiologist diagnosed it as benign I would not worry. Now if you have not seen a cardiologist you should. A good rule of thumb is that if you are a young adult or child, have a normal exam, normal ecg, normal heart by echo and the arrhythmia goes away at faster hr's you should b ok.