Best way to maintain(develop, test, deploy) a medium scale Prosite network MU site

I have had a few small scale blogs where I dabbled with coding/internet. but then I discovered WPMU (pure awsomeness – so much power without having to worry about dependencies between plugins!!) and working to launch a multisite/prosite network finally on my ideas. I wanted to get some best practices from the gurus here on maintaining the site – dev, test, deploy for mu network – anyways wordpress is not great on that – but a prosite network makes me nervous. I have gone through some documentations : here, here and here. But want to hear directly from the horses mouths..Essentially i want to maintain it in an agile mode, relasease and itrate – hence need the extra insights.