You are aware that the wall to the neighbor, which is shown in the picture as about 60-70cm, is actually 1.50 - 1.80m high? This view is then a bit too optimistic...
If the neighbor's garden on the left side is not nice, just create a planting strip there and a nice hedge.
I don't see the budget as too critical. Since there is no basement and the equipment will probably be rather low standard. At least I don't read anything different. With a lot of own effort and individual contracting, something like this is feasible. The land is handled separately anyway.
The floor plan is a failure, most of it has already been pointed out. I would go over it completely again.
Otherwise, good luck.
I don't see the budget as that critical. Since there is no basement and the equipment will probably be lower standard. At least I don't read anything else. With a lot of personal effort and individual contracting, such a thing is feasible. The land is separate anyway.
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You forgot earthworks. On a flat piece of land, it could work