Which means it'll be at 1/4G after you travel a further half light year.

That's a hell of a lot of energy. (If I'm doing the math right, the potential energy difference is on the order of ~20% of the rest mass at the event horizon)

Yeah either the calculator is wrong or I don’t know what I’m talking about. Gravity at the surface of the black hole or the event horizon may well be 1G but all world lines point towards the singularity. I think what is missing is a sufficiently large black hole would have a really low average density at the event horizon thus you wouldn’t get speghettified instantly due to the huge discrepancy of gravity on different parts of your body.

Yeah, black hole "radius" (not volume) grows linearly with it's mass. So very heavy black holes aren't that "dense".