Nuclear being staggeringly overregulated is the reason for the high costs. If we put the same price on lives lost to car accidents as we do to lives lost in nuclear accidents (which some basic back of envelope calculations using old reactor construction costs and lives lost in nuclear accidents reveals to be well over a billion dollars per life) none of us would drive.

If you consider the possible extend of a major accident - whole southern Germany could become contaminated and tens of million of people could loose their homestead - a certain emphasis on safety is welcome.

Building them in series tends to make per-unit cost come down.

Surprisingly, experience has shown that building more nuclear plants, even standardized, don't make them cheaper to build but more expensive.

2010: https://www.sciencedirect.com/science/article/abs/pii/S03014...

2020: https://arstechnica.com/science/2020/11/why-are-nuclear-plan...

In the 2020 article two of the 3 reasons listed are changes, regulation and design changes. So it's not really series-production of a single model.

Yes, that would be to expect. But to determine the feasibility and calculate possible savings with further units, one would have to finish the first of the series first.