Given that this is new construction (so assuming energy efficient) and that you live in Texas (hot, humid) the equipment proposal sounds over-sized. They are proposing 7 tons when roughly 5 tons would appear more appropriate. Don't do anything until they justify the sizing with a detailed load calculation. Get the manufacturer names and model numbers fo the equipment they are proposing.

Propane is generally the most expensive form of heating. Have you considred a heat pump?

"All were the same except the SEERs"

It is highly unlikely that the same equipment with the same sizes has the same SEER rating. You need to get a list of all the model numbers of all equipment you are being quoted.

You should also need to ask for a load calculation to verify the equipment is the correct size. When it comes to HVAC equipment too big is just as bad as too small.

Thanks! I will definitely ask about the load calculation.