In reading your posts my primary concern is your comment about your age? You think you aren't a youngster at 48? The hardest part of this build is going to be the mental load. Start thinking like a young man, which you are. You'll need that later.
You mentioned railroad ballast rock for driveway base? If it's what I think it is I would not use it. It doesn't create a solid base. It continually moves. That's by design. It's intended to move every time the train rolls over it, always working it's way under the ties. I've saw it tried several times, always with poor results. Maybe if you laid it, then put crushed AG lime on it to stick it together?? By the time you do that you might as well buy 2" or 3" limestone gravel.
We just finished a shop building and a house building. Both on concrete slabs. Builder said it was cheaper to build them with 2x6 studs than pole building design when the ultimate goal is insulating and finishing interior.
I pay close attention to Eddie Walker's comments in these discussions. He's direct and blunt. He's very experienced and non-biased in his offerings.
I agree you might not be a good candidate for radiant floor heat. If we get an extreme weather change our buildings overrun a couple degrees. Your cold spells are short enough that you can weather them with almost any heat source. We have an HVAC system with air to air heat exchanger. I think something like that would serve you well. Your secondary furnace would rarely kick on. 95% of your heat would come from the air to air exchanger. They are very efficient to run.
Regardless of heat source, insulate your concrete slab. Minimum 2" pinkboard. It's a bit pricey, around $25 per 4x8 sheet. But it will return the investment down the road.
In regards to hiring labor. I agree with you. Do everything you feel competent to do. More importantly, honestly evaluate your competence and hire what you don't feel confident about.
In regards to your property boundaries. You mentioned bordering a wildlife area? Government owned I assume? Regardless, know exactly where your boundaries are. Last thing you need is the owner of the adjacent wildlife area serving papers on you because you brushcut some exotic weed on their property!!!! Depending on the type of wildlife area you may also deal with hunters wandering onto your property.
I'm excited for you and your family. This will be a great family project. An excellent opportunity to involve your kids and get them outdoors.
Thanks for starting this thread. It will have a large following.