Renewable Energy Communities (RECs), introduced by the RED-II EU Directive, represent a promising mechanism to facilitate the integration of Renewable Energy Sources (RESs) in compliance with European targets. Based on the principles of virtually shared energy and geographical proximity, RECs enable energy exchange among members without direct physical connections, relying instead on simultaneous energy injection and withdrawal through the public distribution network. This paper presents a comprehensive methodology for both the optimal design and management of RECs, improving their technical and economic performances. The optimal design identifies the best mix of REC members and determines the appropriate sizing of Photovoltaic (PV) and Battery Energy Storage Systems (BESS), aiming to minimise the total costs (purchase and installation costs, operation and maintenance costs, electricity costs) and to maximise the incentives on the shared energy, considering also Electric Vehicle (EV) charging infrastructure. Regarding the optimal management, a bi-level Energy Management System (EMS) is proposed. The upper level, controlled by the REC manager, seeks to maximize the shared energy, while the lower-level EMSs, located at members’ premises, perform detailed resource dispatch under both cooperative and non-cooperative behavioural models. Optimization results highlight that including mainly larger members improves economic viability, while the inclusion of a large number of residential users may not always generate benefits, due to increased REC management costs.