The sweet spot would be a fissile material that can sustain a chain reaction but is not radioactive at all. Unfortunately, such an isotope does not exist. 235U and 239Pu are the next best thing.
Not at all, plutonium is essentially safe enough to eat. Fissile isotopes require free neutrons to undergo fission. The dangerous components of radioactive waste are the fission products. When I break apart a large nucleus in fission, I get random configurations of protons and neutrons as a result. These rnadom configurations are very likely to themselves be unstable.
Plutonium is definitely not safe enough to eat, it’s chemically highly toxic. A nearly immediately lethal dose is estimated at around half a gram, though that is mostly due to the radiation effects.
