I emphasise that an entity can be a substance with respect to one property, and an individual with respect to another. If I eat a kiwi fruit, I'm eating it as a substance.
I'm not sure that's right. If you're eating _a_ kiwi fruit, then you're eating it as an individual. If you are eating kiwi fruit, then you're eating substance. In fact you may be describing the very same situation, but the descriptions are different (and not equivalent).
I think an individual can be treated as a collective of one, and not as a fundamentally distinct type. Hence in 3rd ExSol:
le su'o remna le pa remna le za'u remna
and le tu'o remna for substance.