Pro Sites plugin server requirements please.

It's great that Pro Sites can build sites like Edublogs, but we are concerned about the performance and server requirements.

As we once run a local news paper online edition, WordPress seems takes a lot of server resources. What kind hosting requirement is needed?

Could you give us some idea?
1000 users RAM:
2000 users RAM:

800 concurrent users....

What can we do to ensure the heavy traffic will not bog down the whole site, please.

Thank you very much for this and other wonderful plugins!