What m Ramsey said. A variable speed blower is usually a good idea.
Besides doing a load calculation, if you are in a high humidity area,
the contractor should pay close attention to the Sensible Heat Ratio
(SHR). That determines how well the system dehumidifies.
Make sure you replace the indoor coil with the air conditioner, they
are sold as a matched set.
Make sure the contractor will measure the air flow when done with
accurate instruments, not by holding his hand over the grilles.