If the tip is valid, it would make Morgan Stanley the latest in legacy financial groups looking to open a doorway for institutional investors to enter the cryptocurrency market. Despite false reports claiming that Goldman Sachs had put hopes for a bitcoin strategy behind it, the bank has a strategy desk in the works, a service that, if opened, would add to the bitcoin futures options it facilitates for its clients.
Maintenance Margin - this is the % of the position value you have to have in your account at the very minimum to avoid being Margin Called. In some exchanges, margin call will mean you get notified and must deposit more margin to avoid liquidation (like CryptoFacilities). On other exchanges you will at this point be liquidated out of your position. So if maintenance margin is 5%, then the 0.05 BTC of your initial margin will need to be kept for the position to be alive.
There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.