I have a very traditional B&B in a county that did not define B&B in the county zoning ordinance. Before I could do anything else, I had to go through an appeal process to obtain a zoning variance to get permission from the county to open a B&B. The "catch 22" is that by obtaining zoning, the reconstruction I did on my 50 year old house was no longer residential remodeling. It had to be done under the current COMMERCIAL building codes. Even my ceilings were 2" too short. Long story short, after a complete and total revision of the floor plan including a new addition, and submission of two building permits to the state (one for addition, one for remodel even though it was the same project), the architect and the county building commissioner (an appointed official who is in charge of inspecting buildings before they can be occupied) came up with several work-arounds so that I could avoid gutting the entire house.
If there had been a different local building commissioner who had a different view of how the world works, I might never have been able to build my B&B. In so many places the ultimate thumbs up or thumbs down rests in the hands of one guy who may or may not value sustainability the way you do.
I would predict that you will encounter obstacles to this project that you have not yet even imagined. I can't tell you which officials in your locality would have to be sympathetic, but I can tell you that the commercial code book is not online as are most other state and county ordinances. When you think about picking out the state that you'll locate in, or even where you are living now, I think you should find a school of architecture and see if anyone there has experience in what kind of building codes you might encounter, and how difficult it might be to be in compliance with those codes, if anybody there at the school has actual experience building this kind of building.
Albuquerque has some adobe B&B's. There's one out there with adobe in its name. You might contact her.
In the retreat's case, she had owned the property for decades and was known in the community. That might have been to her favor in getting permission to open the center. You really should contact that lady to see how much trouble she had when she opened, or (no offense, Arky) if she's actually operating under the radar, so to speak. See what kind of liability insurance she carries - that might be too up close and personal a question to ask.
Building a code-compliant building that can be insured for the proper liability of keeping guests safe should be one that has plumbing, electrical and HVAC done as well as could be done by licensed contractors. Will your building inspector come out and check off the work you do at each step of the way, or will you have to hire licensed subcontractors, costing more and taking time away from your day job to make sure they show up when they're supposed to. I have some doubts that you would actually be able to save too much money that way.
Here in the midwest, we think of farms comprising hundreds of acres. In our county, if I wanted to sell off a piece of property from one of my farms to build a house on, the zoning would not allow less than 5 acres to be sold. Good farm land here is selling for well over $10,000 per acre. Are you thinking of 1 or 2 acres for chickens and a kitchen garden, or enough acres to grow organic crops for the farmer's market? That is very time and labor-intensive as well. Hard to imagine one couple doing enough lodging rooms as well as a major agricultural project.
I'm not trying to be negative. When I first started on my innkeeping journey I spent innumerable hours researching. Lots of my ideas were discarded. Eventually I ended up with the place that works for me..