Give the completed sale much more weight than the three listings; asking prices only show seller expectations. I wouldn’t apply one flat price-per-square-foot adjustment, because the value of extra area depends on layout and usefulness. Start with the sold property, compare room by room, then...
The main caveat is the refinance assumption. A plan that works only if cheaper financing is available in three years carries obvious rate-reset risk. Run the payment after the fixed period under less favorable rates and see whether it remains manageable. Also compare any early-repayment charge...