Beaufort

Three tons is alot of BTU firepower for 1300 sq ft home.

For a coastal location with harsh salt water environment. I would want a seacoast shield rating to prevent problems and extend life.

First choice would be Trane/AmStd brands.

Here is my HP checklist.

Obviously correct sizing is important. If you are unsure, then request a load calculation or even perform it yourself for a nominal fee online.

there are three equally important components-quality HVAC, the install by dealer, and probably the most overlooked and disregarded is the ductwork system.

these are my minimum specs for a new HP system. both outside and inside units should be replaced to have a properly matched system.

15 SEER, 12.5+ EER, 9 HSPF
best matching VS air handler
full BTUs in both cooling and heating for your rated size
R-410a refrigerant(same as Puron)
scroll compressor preferred
electronic demand defrost preferred
thermostat with "dehumidify on demand" feature
staged backup heat strips
new and correctly sized refrigerant line set

you want a thorough inspection of your ductwork system. size, overall condition, supply and return lines, insulation qualities, leak test, etc.

any hot/cold spot issues in your home should be addressed.

I would only use authorized dealers for the various brands that provide quotes.
see mfg websites.

I would look at Trane/AmStd,Rheem/Rudd,Carrier/Bryant.

Depending on your location, I would not purchase a new HP system that did not have electronic demand defrost.

IMO

Do I have to have 2 units, or is it better to have separate units for both floors?

For best comfort, it is preferred to have two separate systems over one system even with zoning controls. With that said, your living space is relatively small.

Discuss options with your dealer.

IMO

Ok, one last issue before I post the four quotes...today a Trane salesman inspected our unit, and questioned whether our first floor inside unit had ever been serviced. It lies horizontally in our closet, and he said there was not enough clearance to clean or repair the coils. The unit is wider than the access space, and he wants to install an upright unit in another part of the closet, where we will lose some space. Is this true? The other companies did not mention this...even one American Standard Company rep I got off their website...

Ok, one last issue before I post the four quotes...today a Trane salesman inspected our unit, and questioned whether our first floor inside unit had ever been serviced. It lies horizontally in our closet, and he said there was not enough clearance to clean or repair the coils. The unit is wider than the access space, and he wants to install an upright unit in another part of the closet, where we will lose some space. Is this true? The other companies did not mention this...even one American Standard Company rep I got off their website...