I currently reside on a beautiful piece of ground out in the woods with a large creek running through the back yard. Unfortunately I cannot build on this lot without spending $50k+ on water hookup and fancy septic system. I don't have a spare $50k in my pocket.....
Solution: We parked a 36' 5th wheel (allowed), built a cover over it (tolerated) and moved in. We collect rainwater for domestic water and have a composting toilet.
Then we bought another 5th wheel and "remodeled" it. The remodel included removing everything from the frame except the axles & suspension. Then we built a 10'x20' structure with a loft on the lower portion of the frame and a 10'x10' section where the bedroom had been. Net result: about 400sq ft of usable space. Then we put the tail lights & license plate back on.....
I did also live in my last bus for 7 years but most of that was mobile.
Not exactly living in a bus stationary but between the two I think I have a pretty good handle on the lifestyle.
I would look around your county for any indication of tolerance for people residing in RV's. Where I live, you have to get out in the country a bit to find places where it is tolerated. At that if you get the county's attention they will tell you that you can only spend 6 months of the year "living" in your RV on your lot. Solution: I have another rig on the other side of the state and "officially" I move back & forth. The reality of it is there are probably 30+ full time occupied RV's within a mile of where I live.
IMHO: your choice of a composting toilet is right on the money. Dealing with our black tank was one of the biggest challenges before we went to a composting toilet.
I don't know if rainwater collection is a good option in your area. Google may be your friend there.
I don't know where you are, so off grid power options are difficult to pin down. If you are in a place where it plays well then you are in good shape. The cost of solar panels and gear has dropped significantly in the last few years. I am planning on 1000-1200 watts on my bus. Solar panels can be had for as low as $0.27 per watt if you really shop. More common pricing can be $0.50-$0.75 per watt.
I will quit rambling now.....
Best of luck!!