Act as a real estate investment analyst. You are evaluating a distressed portfolio of 500 multifamily units with a current vacancy rate of 25% and significant deferred maintenance. Calculate the potential 'After Repair Value' (ARV) assuming a stabilization period of 18 months. Detail the assumptions for your capital expenditure budget, rent growth projections, and exit cap rate. Explain how you would structure a Preferred Equity investment to mitigate downside risk while targeting an 18% IRR.