In the face of the pressing climate crisis, a pivotal shift towards sustainability is imperative, particularly in the transportation sector, which contributed to nearly 22% of global Greenhouse Gas emissions in 2021. In this context, diversifying energy sources becomes paramount to prevent the collapse of sustainable infrastructure and harness the advantages of various technologies, such as Fuel Cell (FC) Hybrid Electric Vehicles. These vehicles feature powertrains comprising hydrogen FC stacks and battery packs, offering extended mileage, swift refueling times, and rapid dynamic responses. However, realizing these benefits hinges upon the adoption of a rigorously validated simulation platform capable of accurately forecasting vehicle performance across diverse design configurations and efficient Energy Management Strategies. Our study introduces a comprehensive microcar hybrid prototype model, encompassing all subsystems and auxiliaries. This model incorporates a validated FC stack Digital Twin, alongside an experimentally characterized Li-Ion Battery Pack, thus faithfully representing the real prototype. Moreover, the integration of this model has proven indispensable for design optimization, enabling precise performance estimation across various powertrain configurations. After the analysis of the experimental Pulse Discharge test and the calibration of the battery equivalent circuit with three RC branches, we comprehensively examined both single (2-kW) and parallel (4-kW) architectures, utilizing two FC stacks, on a reference driving cycle. Notably, the combination of two parallel stacks emerged as the most promising, yielding a 6% increase in estimated range. Our findings underscore the significance of this innovative approach in advancing sustainable transportation solutions.