Dev/Production portal

I’m evaluating WP as a possible commercial app for my company and one of the things we need is an elegent promotion solution.

As I understand we may have clients with multiple sites and they would be needing to maintain them through a single administrative portal. Can this be done in WP?

If so … say we have a production environment whith a live site and we wish to add a second with (content/design) already in place that exists on a Dev server. Can we do this with a single DB – Can we do this without upsetting the Live DB?