BTC has only around 22 mil coins
BTC has 21 million in total supply, not 22 million.
Coinmarketcap: 21 millionConsidering transaction back-up is not needed (I’m inclined to say that as a lot of trades aren’t really on the blockchain - even trades done on crypto exchanges)
When you trade on exchange, especially when you use leverage trades, you don't own bitcoin. The amount of bitcoin in your leverage balance is a credited figure. It will be turned to be a true figure of your bitcoin after you close your position. Or worse when your leverage position is liquidated.