As global warming intensifies, the building sector must adopt environmental- and energy-efficient solutions to mitigate climate change. With the advancements in the energy performance of building envelopes and the systems applied, we should aim for operational strategies that are essential to further reduce energy consumption and emissions. With the growing integration of Renewable Energy Sources (RES), Building Energy Flexibility (BEF) is becoming increasingly important. This flexibility is most effective when applied at the scale of an Energy Cluster (EC), where multiple buildings operate collectively to optimize energy use. The overall efficiency of various short- and long-term techniques applied to the Energy Flexible Building Cluster (EFBC) can be evaluated considering energy-, economic-, or environmental-related criteria. In this article, the energy flexibility is optimized for a case study neighborhood consisting of 202 single-family houses in Lodz, central Poland. The examined EFBC is evaluated in terms of its environmental and economic profitability. Each building from the examined cluster functions as a prosumer, i.e., both, energy consumer and producer. Flexibility is quantified through reductions in energy use and cost savings, with optimization driven by the response to external forcing factors: short-term weather and electricity price forecasts. Various operational strategies are considered to enhance flexibility within the cluster, aiming to maximize RES utilization, reduce emissions, and improve grid reliability. The results demonstrate the potential of cluster-scale energy management to support more sustainable and cost-effective building operations. The findings highlight the benefits of more efficient RES usage, emissions reductions, and improvement of grid safety.