Don't obsess on PV solar roof orientation. So long as a roof area is within 20 degrees of true south each direction, this still gives you 90-95% of true south solar power.
I forgot to mention that we are going with a single pitch/mono pitch roof so I will have tons of room for solar.
Mistake on triple pane. In your southern climate, you don't need it in the winter - money spent here is a FAR too long payback. Double pane is certainly enough - but buy good ones, not the locally built vinyl clad cheepos. But you DO need to pay attention to summer overhangs on east, west and southern windows to prevent solar gain (maybe this is where you meant orientation).
Awesome to know on the windows thank you, and yes that is what I meant.
In your area, do NOT insulate slab as you need to bleed off heat in summer. Your ground temps are just not that cold in Mississippi.
10/4, that saves more money.
Outside air moisture and interior humidity are your enemy. Put your dryer in a room with outside air inlet and seal it off with good closing (sealed) door. A dryer pushes some 500-600 CFM per minute out of the house and conditioned air pushed out means that air (humid/moist and hot) MUST come in as house is now a vacuum.
10/4, I was thinking about something like that as well
Two ERVs are a necessity with a tight home of this size. The ones you are looking at are great in bathrooms to vent moisture 24x7 and total also provide about 40 CFM total (low speed). When bathroom/shower is in use (DPDT switch to bathroom light), then HRV goes into high fan speed mode (total 80 cfm).
I'll plan on 2 Erv's
I would still do geothermal for ducted AC . . . . an open loop system. You need to put in a well anyway. That many minisplits gets you into expensive territory. I have recently bought from Ingrams and they have a very nice three ton GTHP for about $3100. Forget the thermal heated floors - you just do not get that cold to justify that cost.
I have no attic space with a monopitch roof, and being on a slab I can't go through the floor for a ducted system, these mini splits are pretty amazing and I think we save money on Install vs the geothermal. The only well I plan to have is a solar powered well pumping into a small water tower with a booster pump if needed.
I would do SIPS for roof as you get everything for not a lot of $ and will be installed in one day (roof decking, insulation, interior trusses, R40 foam and inside OSB). SIPS with 8 inch foam (R40) are easily available. You can get 12 inch, but your local conditions don't merit. You can span up to 40 feet with SIPS. Makes interior layout easy with no load bearing walls needed.
The sips I am looking at are claiming R7 per inch, so I'm thinking of using their 4.5" on the walls and 8" on the ceiling/roof. Polyurethane Structural Insulated Panels | Energy Efficient Eco Panels SIPs - About Eco-Panels
Infiltration is your enemy - not heat or cold. Build yourself a temporary blower door (or window) with an old HVAC squirrel cage blower and simple water manometer. I use dry ice for "smoke" to detect leaks.
I got a huge 4,000 cfm greenhouse fan 
If you are in a rural area, build a pond (discharge water from open loop geo unit into this) as this markedly lowers your home insurance. Home insurance goes WAY up in rural areas with volunteer fire departments. You will also get a discount for metal roof (good idea). A fire pumper can dip suction hose into pond. Pond got me a 30% discount on my home insurance . . .
I'm a fireman, I am looking into a small pond, but I think if my water tower can hold 1,500 gallons I can get away with that as well.
Do you really mean "as efficient as money will allow"?
Yes
Why a fireplace? This is a true energy waster. Put in a good wood burning stove that has opening (and closing doors). You can see fire if you want to, but can close it up for more efficient use. - but make it small (24 - 36 KBTU/hr) as it will otherwise overheat the house.
I should I have been more clear, wood burning insert is the plan, we like the look of the brick and the fire.
Mazel tov!
Thanks
Steve