Why do you need a broker for cryptos? Just do it direct through an exchange like everyone else. The software/charts for cryptos are excellent and are free. Real-time data is free Kraken and Poloniex are 2 popular exchanges. Yes, you can short it the same as spot FX, i.e sell one currency, buy the other.
If you own a crypto currency, I was told that it resides on your computer. If that is true, what happens if you loose your PC or it gets damaged and you can't access your currency? Can you back it up?
The wallet, www.multibit.com can be copied to another pc or multiple usb drives, just don't forget your password and make sure it is very long. You can also print them out but don't lose them!
Similar risks hold for any physically held peer-to-peer stored instrument. Cash can be lost, gold coins can be stolen, bags of coffee can be damaged by flood, the disk that holds your crypto wallet can crash. At least crypto can be backed up; no way to back up gold bars! Maybe insurance... I wonder if anyone is selling cryptocurrency insurance? Can I buy a policy to protect against loss of my bitcoins?
You can short BTC, depending wich "exchange".There are even leveraged BTC. About wallet it is said you could in some cases storage the "data" in a usb.Anyway I could tell you some issues aswell =)