Centrelink has embarked on a Regional Microsimulation Modelling Project. The modelling work is being undertaken jointly with NATSEM. The purpose of the model under development, the Customer Service Projection (CuSP) Model, is to provide a tool that will assist decision-making through short to medium-term projection of customers and channel use demands at the small area level and under alternative scenarios of customer numbers, customer characteristics, access preferences and opportunities. This paper describes the methods and techniques used in the CuSP Model, and highlights a number of particular issues encountered in this major extension of microsimulation modelling. These include issues with the extensive use of administrative data, spatial units and small area projections, customer behaviour and, importantly, the process of model development.