In large-scale metal composite systems, comprising independent plated components coupled along weld lines, the response and encountered failure modes are governed by complex interactions of local instabilities with the spread of plasticity. The system scale, as well as the requirement of achieving mesh conformity throughout the domain, pose severe limitations on the modelling front and increase the associated computational demand substantially, thereby rendering extensive nonlinear analyses prohibitive. This work is motivated by the necessity for a versatile modelling strategy, enabling the accurate nonlinear response evaluation and assessment of large-scale composite systems under extreme static and dynamic loading. A high-fidelity modelling strategy is proposed, which enables the accurate response evaluation of composite systems in the range of large displacements, taking due account of geometric and material nonlinearity. The strategy utilises co-rotational Reissner-Mindlin shell elements, with an embedded hierarchic optimisation approach that addresses inaccuracies arising from locking phenomena. The proposed modelling approach is further enhanced with a dual super-element domain partitioning methodology, facilitating scalable parallel processing in High Performance Computing systems with distributed memory, which enables a substantial reduction in the computing wall-clock time to be achieved and potential memory bottlenecks to be overcome. A systematic methodology for surface coupling along a line is developed, based on a novel 1-D coupling element formulation, which facilitates discrete constraint enforcement between surfaces of arbitrary relative spatial orientation discretised with non-conforming finite element meshes. The approach is applicable to any type of 2-D and 3-D elements and provides a systematic framework for geometric modelling of weld lines, coupling of independently discretised regions within a system, as well as for domain partitioning problems involving computationally heterogeneous partitions. Efficient translational and rotational coupling element formulations are further established for surfaces discretised with quadratic Reissner-Mindlin shell elements, and their performance is extensively assessed through patch tests, sensitivity analyses and verification studies. Several application studies involving extensive nonlinear analyses of geometrically complex, large-scale, composite structural systems are presented, to illustrate the versatility and computational efficiency of the unified modelling framework, encompassing partitioned high-fidelity finite element modelling and the developed coupling capability.