Previous years qadha fasts and kaffara for breaking a fast intentionally

Q: As Ramadhaan is nearing so I thought of covering up all my Qadha roza but I don't have the exact count of the Qadha roza. What should I do in this case? Also I have Qadha roza of the previous few years and I don't remember how many they are. 

I had once broken my fast when I was young but baaligh, but I did not know that it was a major sin. How do I cover up for that?