Multi Site Dev -> Live Flow

I am looking for some suggestions. We are setting up a multisite network for individual client sites. We will be custom designing each site and then using domain mapping to host on individual domains.

Now my question is, what is the best way to organize a development environment for creating the custom sites and then moving it to the live environment without endangering the other live sites.

We were discussing using SVN? Would this be useful or a hindrance?

Any recommendations?