Menstrual cups

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Hi Ladies 
I just wanted to ask, do some of you still wear a pad or panty liner when you use a menstual cup for security? 
I'm a heavy flow type of girl, and I'm worried the cup won't hold my flow and leak occasionally. This is my first cycle using them.
 Also could someone enlighten me on what the difference between the small and larges cups are, how you store them (on the go or at home) and how you sterilise your cup. I have watched YouTube vids but they are all pretty much the same. 
Thanks 💜