So if bitcoin and cryptocurrencies are open for the world to see because of blockchain, are there any charts that show the "wealth distribution" of the coins? So if you wanted to determine that like 40% of the coins are held by 1 entity or if it is a lot more spread out than that? Is that research already done anyway? If so, where could I find it?

I see that there are numerous exchanges like gdax and bitfinex, etc. but why should I use one over the other? I get it if one has lower fees but is there something else that would make one attractive?

Is it about the tools they offer? Is it the volume available?