Massive in this context means the mass of the planet, not its radius. So it has the same radius (or volume, or takes up the same amount of space) as Neptune, but it has 4 times the mass (or 4 times the stuff inside of it).

Yup. This is why the whole ‘States rights’ argument is absolutely bullshit. The only states trying to bring the federal government in to usurp other states’ authority were the slave states.

You’re probably right about it not saving enough money, but the math you did above assumes one water heater per person.

The median household in the US is about 2.5 people. So $34 per year per person becomes $85 per household. Reducing the time to break even to 17.3 years.

Still longer than that water heater is likely to last, but not quite as bad.

Radioactive elements were formed in the last moments of a collapsing star, so even those were formed during fusion.