Mortgage Overpayment

If mortgage rate > investment return, yes. 6.5% mortgage vs 4% bond returns → overpay. But 6.5% mortgage vs 10% stock market expected return → invest elsewhere.

No. Credit card rates (18%–25%) far exceed mortgage (6%–7%). Pay credit cards first. Mortgage is the cheapest debt; pay it last (strategically).

Yes, but refinancing costs $3–6k in closing costs. Break-even is 18–36 months. If you plan to stay, refinance. If overpaying for rate, overpay instead.