I like William's idea about the geodesic greenhouse outer envelope, though the hot, humid four-season hothouse that some would employ would cause issues with any straw bale construction, or at very least require extensive humidity controls. There are some issues I can see with your approach, though, Heather.
I think it would be helpful to know why you think a geodesic dome is a good shape for a house for you, considering the climate.
I also wonder if you have checked out the history of building in your area. Do you know what the predominant forms of
shelter were before the European arrival? Looking at these, and at what was built and discarded over the years after Europeans arrived, might give you some really good clues about designing a structure to fit your needs that is better suited to your particular climate.
Geodesic dome houses are inconvenient for the same reason A-frame houses with really steep roof pitches are inconvenient: when we try to fill these structures with furniture, we end up with lots of wasted space, and not
enough vertical walls against which to place furniture. So you either end up with furniture unanchored by placement against or with reference to walls, or you end up building internal walls, but that both wastes the space taken by the wall and the space you're cutting off to make it straight, leaving you with awkward crawl spaces and haphazard storage areas.
Geodesic domes as a structural shape only benefit you in terms of efficiency of heating. In the American midwest where you are, how cold does it get in the winter?
In addition to this, building materials mostly come in long, straight pieces or 4' x 8' sheets, and are usually flat in at least one dimension. Finishing materials are designed to fit these parameters. This suits geodesic dome building not at all.
Imagine trying to cut 4' x 8' rectangular sheets of glazing of any real substance into hexagonal panels to fit your greenhouse structure. Unless you're using flexible, transparent house wrap, which is unlikely to wear very well or for very long, it would probably prove to be a very wasteful process, costing a lot just on that basis.
Now imagine that happening through every stage of your geodesic straw dome house build.
As to some of your other points, treating wood to withstand soil contact by modern industrial methods is a toxic process in most cases that only lasts the life of the wood product because after it leaches out of the wood foundation and into your soil, it is free to rot away like any other wood. Treated wood is usually avoided as much as possible by those eating food out of the soil they grow.
By comparison, cinderblock is more durable, more insect and fire-resistant, and won't leach literal soil poison into the ground. In addition, they can sometimes be salvaged whole from a demolition, or can be purchased used for a discount, in some situations.
Isn't the American Midwest where the common complaint about the summer is that it's not the heat, but the humidity? We get that in Toronto, believe it or not, due to the humid continental climate, and I wouldn't try building a straw bale structure here, either. All that humidity will get at the straw, unless you take extensive or toxic measures, which defeats the whole point of using a relatively cheap renewable as a building material.
So I would probably suggest rammed earth, but compressed earth block is also good, and some would advocate earthbags. If you have a lot of structural lumber and don't have anything better to do with it, you could look at Paul's WOFATI idea. I actually love the WOFATI concept, but I will do it with rammed earth and/or compressed earth block, and/or maybe earth bag, depending on the situation.
Back to the geodesic greenhouse as an outer envelope, there is a product being used to house a educational and recreational biome
project in the UK (like a zoo, but for different biomes around the planet), which creates a geodesic greenhouse by inflating hexagonal panels of a UV-stable flexible transparent glazing. This, in my opinion, is the best idea to ever be applied to geodesic domes. If they were affordable enough, a family could simply drop one over their farmhouse, barn, and surrounding yards, essentially enclosing their zones 0-2, perhaps even 3. You could keep a constant humidity and temperature, and although it would likely still be too humid to be appropriate for straw bale, any enclosed structure would instantly be buffered from severe weather and changes in temperature, reducing maintenance costs and extending the life of materials otherwise worn down by exposure to the elements.
Good luck, in any case. Let us know how it goes.
-CK