DoS attacks are really easy against Tor hidden services. The service can't block the attacker because all clients are anonymous. Tor hidden service introduction points can sometimes also be DoS-attacked. I wouldn't use Tor to run a site like this.
Sorry, but its a bullshit. ddos attacks on Tor isnt effective because of connection latency (ping is from 1 up to infinity seconds).
Defending from attacking bots making 1 connection per second isnt a problem.
The problem is to run Tor software on large botnet for attacker.
Sorry, but that's bullshit. Latency does not make one lick of difference if one physical computer can create as many simultaneous requests as it is capable of sending with no way for the server to detect they are from the same machine. Now imagine 1,000 such machines and you have a very small botnet taking out silkroad.