Detailed dynamic modelling of large-scale power networks is becoming increasingly relevant as the share of inverter-based resources increases, introducing a multitude of power system stability problems. Faster system dynamics are often overlooked in conventional phasor-domain analysis; however, electromagnetic transient (EMT) models can capture instantaneous voltages and currents, enabling accurate representation of converter controls and protection systems. Even though plant-level modelling can be performed and modelling/grid code requirements met, large-scale EMT modelling for system-wide stability analysis remains challenging. With this backdrop, the paper proposes a systematic model and network reduction based approach to enable EMT modelling of large power networks for high solar/wind integration studies. The dynamic modelling process follows a staged approach, aimed at obtaining a reduced extra-high-voltage network and gradually including selected high-voltage zones, utilising the aggregation of coherent generations and network-reduction approaches. The modelling process also includes relevant data collection, model initialisation, parallelisation and validation steps. The reduction enables analysis of dynamic stability at key parts of the network without representing the entire system or its component models. The proposed method is validated on the Kundur two-area power system and the IEEE 39-bus system, with the goal of applying it to the future network model of the Irish grid.