This is a great place to start working on Wordpress, Wordpress can be very daunting, especially if you plan to setup more than a website.
WPMU has a great set of plugins that enable ideas, helps manage and reduce confusion. They have a great community, blogs and tutorials.
If you looking to save tons of money from going up in smoke, wpmu and it's great set of products will definitely get you started ok that path.
I highly recommend WPMU, a must have for any Wordpress freelancer. If you don't have this you don't have superpowers.