What's the optimal configuration for a large WPMU network?

I'd like to enquire about the optimal configuration of a large multi-site network.

Could you please clarify:

- Can each multi-site have its own cPanel account?
- What is the recommended configuration for WPMU on Apache, where can I find tips on optimising performance etc?

Additionally, we're looking for somebody to set up a clustered infrastructure (strictly for WPMU), i.e. 3 virtual servers and two database servers? Who could you recommend for this (paid) work?