ask for a load calculation in writing for cooling and heating broken out for each zone. One should assume you will have excellent building qualities, insulation, doors, and windows. Heat pumps/ straight AC?...5.5 tons works out to about 725 sq ft/ton....for SC location, you want good humidity control and for the upstairs system, you don't want to be undersized.

IMO

Contractors generally oversize HVAC systems so there won't be any chance of "it not being big enough". 725 sqft/ton doesn't sound too small for new construction - any bigger and you might compromise dehumidification. I'd just confirm with your builder that a load calc was done and that the heating and cooling loads match the equipment size.

get the load calc in writing so you will have it documented that correct sizing matches the load...that's the professional way to approach your concern...and if a problem does occur, you will have the documentation to fall back on...

IMO

I want to say thanks to all of you. I will request the load calculation from the builder.