Address the challenge of reducing urban housing costs while maintaining neighborhood character, accommodating population growth, and ensuring economic viability for developers. Analyze this problem by identifying all key stakeholders, their competing interests, and the constraints within which solutions must operate. Propose an innovative multi-faceted approach that addresses these tensions through policy, design, financing mechanisms, and community engagement. Your solution should include implementation considerations, potential unintended consequences, and metrics to evaluate success over different time horizons.