I can store the tick data, although I'm not storing it at the moment (I disabled it for the launch and will test the load that enabling it represents).

I use Cassandra with just 1 node for the moment.

It's kind of that, although the client doesn't talk to the exchange directly, it only talks to the backend. The backend consumes events from the different exchanges, transforms it to a common format, stores it and serves it to the client (in brief terms).