Essentially what are the legal requirements for starting the next Binance, Bittrex etc. When I say in the United States I mean US based customers (preferably registered in the US as well.)
I don't agree that the US government hates cryptocurrency or crypto exchanges, though I will say that the USG is still unsure how to manage crypto.
The legal requirements vary based on what state you are trying to set up an exchange.
Current Federal law puts regulation of crypto under the jurisdiction of the Commodities Futures Trading Commission. While the Securities Exchange Commision has brought some enforcement cases forward, the courts as of now have sided with the CFTC. So make sure you are following those requirements.
At the same time, each state has (probably, but I can verify) their own registration rules for anyone that participates in bitcoin (i.e. mining, trading, selling, or thinking about mining, trading or selling etc). Many states are taking a second look at those rules as crypto grows in popularity and as regulators figure out how to regulate it appropriately. For example, NYS has registration rules, but it also has legislation that would form a task force to evaluate current rules and propose changes. NY also had the first locality ban cryptomining (Plattsburg), so that will also be part of the discussion. It is timely, as some of the big Wall Street players are looking at launching U.S.-based exchanges.
Incidentally, NYS also has legilstion to study the possibility to launch its own cryptocurrency. That could get interesting.
Hope that helps. Happy to set up a call to chat more about any specific state regulations.