The network structure is still debated. For now a client/server architecture is the target. Think of it as a crypto-napster. As the amount of communication is fairly low, running the server as a hidden service in the tor network is an option. As with any client/server architecture, the clients can decide to use tor for their incoming connections in any case.

There will be support for a credit system. Each successful lookup gives you credits which you can use to do a lookup yourself. You can sell those credits for real world money to compensate the investments you made for generating the tables. If everything goes statistically well, then you have to make N lookups yourself to do one of your own lookups involving N other nodes.