I just built a few years ago & can share a couple of thoughts. One is that NG, electrical, solar, & propane costs are highly regional and location specific. Not only do the basic costs of energy vary a lot, but they are also subject to being changed taxed and surcharged at every level of politics. You can't do much about the cost of energy, but you can stay flexible by deliberately designing in a way that keeps your options open.
I don't know about Kentucky, but here in the rural west, along with politics and variable energy costs, even our normally reliable winter & summer climate isn't so stable anymore. You say you want to design for 30+ years, but what will it be like then?
In the Rocky Mountains we don't seem to be having much of a winter for the last few years. Little snow, but more rain than usual means that drainage has become the issue that plowing snow used to be. In fact, the unstable weather is what got me to thinking about flexible design. I've lived here 50 years, and finally got the tractors all set up to deal with deep snow - and since 2013 haven't had much snow. Instead, we had to re-design for rains & drainage.
This year the ground hasn't even frozen hard yet. Yesterday I noticed that little bitty grasshoppers about 1/8" long were hatching out in large numbers. Both the grasshoppers and flying bugs are already out.
Here's an example of what I mean by staying energy flexible: Are you going to put a wood fireplace or stove or hearth burning NG in the living room? Those are great for backup heat and for aesthetics. And finished fireplaces and some stoves can be expensive enough that you might want to hold off on them right now. But all of them use the same kind of chimney - so this is the time to design a chimney into the new build. If you think a chimney is expensive now, you are right....it sure is. But just compare that with adding one later....
What I'm saying is that the times are uncertain, and if you are building new, then why not put money into keeping your options open? A full concrete basement with thick walls & sunk into deep into the ground is not only a great foundation, storage, and storm shelter....but it provides geo-thermally stable temperature for the entire house. And it does that for free just by being in the earth. Free geo-thermal is nice, but what I mean by keeping your options open in the case of a basement/foundation would be to build whatever access points, exterior doorways, mounting points, drainage sumps, hydronic, or geothermal piping right into the walls and floors when the basement/foundation is poured. These options don't cost anything now - most are basically just holes in the poured concrete. But they sure give a ton of options later on. You don't need to install those systems now, but any clever architect can provide all the necessary holes and pads so that you can install at any time in the future. Making it possible - even easy - to do those things in the future costs very little in a new build.
As another example of designing towards keeping options open, I had them put heat pipes into the concrete floor before the cement was poured. Although a hydronically heated floor can be expensive, putting in the necessary piping in case I ever wanted to hook it up added little more than the cost of the special heat pipe itself. This is also the time to consider putting in any necessary geo-thermal mounts or connections as well - even though you may or may not complete the geothermal installation until years later or never.
Upstairs for exterior walls remember that the insulation will determine more about the energy costs than what type of heat or AC that you put in. Look at your coldest and warmest walls and consider what it would take to over-insulate them. Same for the roof. You just cannot have too much insulation and separation between layers in the walls and roof.
What I'm saying is that if you design in your options now, then you don't have to be tied to any one type of Heat/AC for 30 years. If some energy advantage comes along you can go with it.
Good luck...sounds fun,
rScotty
