Planning and Implementation Question

I am trying to develop a multi-site for a start-up with hopes of high expansion and growth. It is estimated that 90% of the sites will be free personal blogs and the remaining 10% will be divided over 3 types. To get momentum, all sites will be free initially free. Currently, blog types is activated. The revenue model is primarily advertising based, with some user sites potentially being charged for added features. We have multi-db installed. From a structural and efficient perspective, since we do not intend to charge for sites initially, should we still implement Supporter at the beginning or can it just as easily be added when needed? What are the trade-offs?