Urban energy systems (UES) design must adapt to the multifaceted challenges of an evolving global energy landscape. This study examines ten critical questions that define current challenges, methodologies, and future priorities in UES design, providing a comprehensive understanding of techno-economic and socio-institutional aspects. It first examines the lateral and vertical interactions across spatial scales, sectors, and time, as well as the evolving needs in heating, cooling, transportation, and renewable integration. Consequently, the study critically assesses the capabilities and limitations of current energy system modeling practices, highlighting challenges related to data requirements, system complexity, scalability, and uncertainty analysis. It then discusses building energy demand and building stock modeling to provide high-resolution analyses of decarbonization pathways and to support effective demand-side management and storage solutions. As these approaches require data, the role of data availability and governance in UES design through the integration of advanced technologies such as artificial intelligence is reviewed. Moreover, it is important to consider dimensions beyond digital tools. The study discusses the inclusion of broader environmental dimensions beyond greenhouse gas emissions into UES planning to ensure sustainable pathways. It also emphasizes the role of governance, policy, business models, and social engagement in successful deployment of UES. Finally, this study analyzes how UES design can enable emerging urban visions and address the unique challenges faced by low- and middle-income countries in the Global South. By answering the ten most relevant questions on UES design, this paper aims to examine the future priorities of UES design and to offer actionable solutions for creating more resilient, fair, and sustainable urban energy futures.