Miners don't process transactions, exchanges do.
No. You store it in an offline wallet. You trade it on an exchange like Coinbase. You don't store it on an exchange because if it's being stored online, it's prone to being hacked and stolen. You can still cash out at any time, you just have to first transfer it to an exchange prior to doing the transaction. The miners have nothing to do with this.
Yes, you are conveniently naming the countries you want to, whether you realize it or not. According to your own figures and the link you provided, the US mines almost twice as much as Iran, and is second to only China. Iran isn't in the top 5, and North Korea isn't even in the top 10. Well yeah, when you take the one country mining most of the bitcoin (China) and then add any other country, of course that combination is still mining most of the bitcoin. You could also say that the majority of bitcoin is mined by China and USA, China and Canada, China and Germany, China and Norway, or even China and Greg Schiano, but instead you only choose Russia, North Korea, and Iran. I also still don't see why this matters--bitcoin is bitcoin no matter where it is mined, it's not a national currency tied to a government.