Not a pro but I'm going through a reno so I've been reading code a lot lately. Fun stuff.
Your #'s dont add up, check this
https://energycode.pnl.gov/EnergyCodeReqs/?state=Texas
Contractor should calculate load with a manual j. Not exact but I think this is a decent estimator,
HVAC Load Calculation - Maunualj - Whole House Loadcalc