Start with efficiency
Harper's overall point about starting with an efficient envelope is dead-on; managing solar gains is going to be a huge part of it down in Texas, and you'll also need to be careful with how you apply insulation and air barriers to avoid trapping water vapor or moisture in wall or roof assemblies. The ultimate test of this is a blower door test that actually measures the amount of air that can leak in and out of your house; this test, along with infrared thermography (which is good at pinpointing leaks), are the bread and butter of home performance analysis, alongside some intuition and understanding of how heat, air, and moisture/water work.
Vented attics and ducts do not mix!
One classical mistake in Southern homebuilding is the use of a vented attic to house HVAC equipment and ductwork. This not only shortens the life of the equipment due to the high ambient temperatures present in attics in the South, but wastes valuable power and capacity on overcoming heat gain through the ducts during cooling seasons, often to the tune of 10-25%.
As a result, if you are using a ducted system, you are far better off putting the ducts inside the building envelope fully, one way or another. "Hot roof" configurations can work well in Texas due to the lack of ice dam concerns there, but basically require a roofing system that can withstand high temperatures. There are also configurations, such as scissor trusses, that form a mechanical cockloft space between the finish ceiling and the ceiling envelope plane aka where the attic insulation lives, if you do not mind the extra structural complexity that entails.
Beware the Ductopus, Strangler of Air Conditioners!
Atop this, Southern residential construction compounds the error of putting ducts in the attic with the aid of a few bags of flex duct and a harried installer or three, resulting in the organic, many-tentacled monstrosity known as a "ductopus" spawning in one's attic. The unstretched flex duct creates excess friction losses, which reduces the efficiency of the blower at delivering conditioned air to indoor spaces, thus forcing further upsizing of the system to overcome this condition.
The antidote to this is proper duct design and installation -- applying ACCA Manual D rigorously, installing the ducts properly, and avoiding the indiscriminate use of flex will give you a fighting chance of being able to use Manuals J and S to right-size your HVAC system for your house, instead of taking the "bigger is better" approach to the problem, because bigger is not better when it comes to HVAC, especially if you are building a high-performance home. Of course, you will want to test your ducts when installed to ensure that the static pressure across the blower is acceptably low; this is a good measure of the overall workmanship of the HVAC techs, as well.
Play to your strengths
Texas is a mostly-cooling climate, by and large. As a result, since you will want some sort of air conditioning anyway, the logical choice for turning electricity into heat here is a heat pump. Furthermore, the use of electric resistance heat is a gross waste of power when your electricity is coming from solar panels; as a result, you will want a heat-pump setup that avoids heat-strip "emergency heat".
This leads us squarely to mini-split heat pumps, of both the ducted and ductless varieties. Instead of leaving the blower on full-bore and using resistance heat to both fuel the defrost process and make up the missing heat, mini-splits stop their indoor blower during defrost, thus allowing them to defrost without burning power in resistance heat strips or blowing cold air everywhere.
Mini-splits also have the advantage of being able to use either multiple ductless heads or low-profile, in-ceiling ducted heads that make going without a full-sized attic or basement to house HVAC ductwork an easier design proposition. There are also full-sized air-handlers available for today's mini-splits if you want to use one to drive a fully ducted system. You do need to be careful with duct design and installation with this approach, though, as their blowers can't provide quite as much static pressure as the ones on more typical split-system air-handlers.
Why not gas?
The issue with gas in a climate like yours is that for you, gas furnaces come in one size: too big! For a climate with light heating loads like yours, even the smallest gas furnaces are going to be vastly oversized compared to your actual needs, especially in a high-performance building envelope as heating loads fall off faster than cooling loads when you add insulation and remove air leakage paths.
Given the comfort and efficiency drawbacks of an oversized furnace (even if it can modulate), this makes mini-split heat more attractive, especially with today's mini-splits that can handle just about anything Texas will throw at them for outdoor temperatures. However, I would not completely discount gas heat: modern modulating-condensing gas hydronic boilers are highly efficient, and can also feed an indirect hot water heater to provide domestic hot water as well as feeding an air-handler coil, radiators, or floor heat for space heating. This allows the boiler to operate in an efficient range year-round while providing efficiently easily comparable to high-end gas appliances for water heating and space heat.