First - Trane (Bryant) has the best rep in the coastal areas. I recently built in a coastal area and put 2 trane heat pumps in for 2 floors.

I also built a larger house with less tonnage than all your quotes. And I had less insulation. Windows and orientation are what matters but 5.5 tons for 2100 sqft is very high - especially for new construction.

The number one problem with HVAC quotes is oversizing...

I'd probably go with 2 units but there are other details that matter more.

As far as furnace, you don't mention what you have available. I suspect that NG is pretty rare in Fl and that is the only fuel where a furnace would make sense. If you don't have NG, you would be a fool to put in a furnace.

Trane and Bryant are not the same product, although Trane and American Standard are. Carrier and Bryant are the same. Differences between sister brands are typically only cosmetic and sometimes warranty.

Oops - my bad. I must have had a cocktail already....

Coastal = Trane/AS.