I think you should reconsider integration of Tor. This is quite likely to end badly for you. If the police reports are true SR2 had 150,000 users: if even a fraction of those decide to migrate to OpenBazaar at some point, any legitimate usage will likely be overwhelmed by illegal usage. That would put you in the unenviable position of being the next DPR, except not anonymous (Silk Road sold books as well as drugs but that didn't matter).

Your best bet is to just not ensure IP addresses are recorded and unobfuscated. That'll help tip the balance towards legal activity.