How bright would the planets look from Pluto?

Neptune at brightest would have an apparent magnitude of +8.29, much too dim to see without a telescope. That happened, for example, in 1979 August, with a Pluto-Neptune distance of 31.05 AU, and Neptune 75.7% illuminated.

I'm too lazy to do the other planets, but I expect that they would be even dimmer. Horizons web site doesn't seem to want to do the calculations itself, but it gives the magnitudes as seen from Earth.

They would look like common stars. In fact even the sun would look more like random star in the sky. The brightest sunlight would ever be on Pluto would be similar to standing under a street lamp on a moonless night.

As you said, it all depends on the position of pluto and the other planets. Also, the sun does not shine very bright that far into space, so looking back, the planets may not seem as bright, but shadowed.

You would almost certainly not even see Venus or Mercury, and the Earth and Mars would just look like tiny dots. You could see more detail on Uranus and Neptune than you could from Earth, and Saturn and Jupiter would look about the same.

You probably couldn't see any of them. You could maybe see Neptune and Uranus. Maybe.

Probably the same as here.