Gary,
BuildItSolar is great!
Better to undersize AC unit than over size.
Over size reduces run time, in high humidity environments the AC unit does not get a chance to reduce the humidity before it meets the temperature requirements, leaving the humidity too high, with you feeling uncomfortable. Personally experienced this, room was cold feeling and clammy, not comfortable at all.
Undersize will not reduce the temperature as much, yet can remove more humidity. Lower humidity provides same comfort at a higher temperature. Just like out west.
High efficiency fan to move air again allows warmer air to feel comfortable.
If solar heat is available and high humidity, Desiccant cooling should be considered in this location.
Desiccant requires just as much energy to dry it as the cooling it reduces, therefore solar heat is required to make this cost effective and why it's not a main stream solution.
To understand the benefit of desiccant cooling check out:
http://www.engineeringtoolbox.com/cooling-dehumidifying-air-d_695.html
The sensible heat (reducing room temperature) is less than the latent cooling (Dehumidifying). Therefore based on the example desiccant could reduce cooling cost 50% with 60% RH air. (half size AC unit)
Most places cool down at night, taking advantage of it can reduce the day AC needs (eliminate)
I believe you have this on your web?: (night cooling)
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1771-08.pdf
Cool water storage at night, with reduced heat gain during the day, coasting through with stored cooling from the night before can be just the ticket, maybe boost performance with desiccant.
Keeping the humid air out of the home is important (well sealed), yet so is ventilation.
My Fathers home in FL has electric heating with AC unit. Looking at the cost of air sourced heat pumps, only couple hundred dollars more than AC only unit, yet it's not used. His electric heating bill in spring / fall is as large as the AC bill in the summer making it more expensive to live in FL than here in Michigan!
I keep my house warm 74F in winter, 77F summer. Total heating/cooling bill is $800/yr, add in hot water, stove, cloths dryer bumps it up to $950/yr. Heated living space 2500sqft (first story + basement)
Have fun,
Scott.