Out of 3000 users, lets say concurrent would be 1500 (means fetching something at same time from database) which I would expect from a 30,000 user site to reach this much concurrency, but, for the sake of satisfaction of enough hardware resources that even all 3000 would be online at same time, you still wont be needing a load balancer for this setup. An Octa core CPU with 64GB Ram would be sufficient.
I couldn't understand the need of setting up two sites, technically its possible but will complicate the setup resulting in data corruption.