How many sq feet of glass facing south and west? Is it solar reflective glass? It probably is.. If not high reflective glass, the best you can get, would be a really good idea on the south and west facing glass, but not the East facing or North facing glass... You want solar heating on the east side.
Efficiency is rated in SEER, (Seasonal Energy Efficiency Rating).. For an AC in your area, if I owned the home, I'd pay 50% more and get SEER 14.
If you have natural gas(not propane), I would go with gas furnaces, 90% efficient max, not 95% etc.. The cost of repairs dwarfs the energy savings in my experience.
From what you have said so far, a total of 6 tons for cooling would be a bare minimum... 7 would be better and I recommend splitting that up to 2 each, 3 or 3.5 ton units (14 SEER) and 2 each 90% efficient gas furnaces, (the cooling coils (A coils) above each furnace located in the basement. Furnaces rated 120,000 BTU's each at least in order to handle the air required for cooling. This estimate is plus or minus 20%.
If I were the home owner, and wanted to keep it below 75F no matter the heat of the day I would be looking, 2ea, 4 ton SEER condensing units with A coils, and 2ea 120,000 bu furnaces (required for air flow during summer).
I'd buy Rheem if I wanted the best for less and ease of maintenance... I don't appreciate the serious complexity the two market leaders provide.. Costs too much to repair, with scant benefits if any... That would be company names beginning with C and T... Those have great promo though.
The contractor may want to provide heat pumps. I don't like them for widely distributed systems. These get double the wear on compressors as compared to what I have recommended above. Package units, heat and cool in the same box, with ducted distribution is not the best in cold east coast climates and puts service men outside in the weather, that is expensive.
Costs in your area will range between $1,500 and $2,500 per ton+. Worthwhile add's are Honeywell automatic wash electronic air filters, if anyone has allergies or smokes. Those are expensive and high quality humidifiers, stainless steel basin type those will improve the family heath in the winter. Buy them over sized, and in stainless steel, don't skim on the east coast, they get a lot of use.