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.