Reducing costs and risks to foster rural electrification in developing countries is one of the major hurdles for researchers, firms and practitioners aiming to develop business with rural minigrids, which are local networks that supply energy demand by exploiting local sources. Predictive rolling-horizon operating strategies have proven to reduce operating costs and better cope with uncertainties in renewable sources and demand than standard priority-list approaches, when forecasts are accurate enough. Their main drawback is the need for more powerful controlling devices, which, however, is becoming acceptable for modern operation purposes. Yet, calculating the optimal design of the minigrid operated with predictive strategies can easily require much larger computational requirements than with priority-list rules. In the present paper, we describe a two-stage procedure to reduce the computational requirements of design methodologies based on predictive strategies. First, an optimization is developed using a priority-list strategy, namely load-following, whose results are used to refine the second-stage optimization based on an advanced rolling-horizon strategy. Results suggest significant reduction in computational requirements, up to 84% with respect to standard predictive approaches, with negligible reduction in the optimality of results.