Key mortgage mistakes to avoid include not getting pre-approved, overlooking credit scores, and failing to compare mortgage options. Buyers should budget for total homeownership costs, including property taxes and maintenance. Skipping home inspections and neglecting closing costs can lead to financial issues. It's crucial to consider the neighborhood and save for a down payment. Additionally, avoid making large purchases or changing jobs during the mortgage process. In Pennsylvania, explore state-specific mortgage programs and plan for property taxes and insurance.