It looks like the standard business model of sell product, receive payment might not be the best idea for something like this, but there are other models.

What if the primary form of business is selling the parts instead? Then repair shops become the primary customer, with home repairs and selling the actual vehicle just being the PR model for adoption?

You say they won't need many spare parts. But thanks to emissions regulations, they'll still have to have plenty of electrical components, and those do still break. Easily.

Even on the old-style tractors, I've still replaced plenty of parts. Things do break. Simple things that are easy to replace, but you still need the parts. Clutches, bearings, etc. Tractors are exposed to harsh environments for most of their lives. Plenty never ever come indoors.

The engines don't often need replacing. But plenty of other things still do.