Your model will be so far from actually being functional in real shoe terms that you’re better off just carving the outsole out of a hard material. handmade shoe “prototypes” always look terrible, and unless you’ve designed in some wild function to the outsole that this would serve as a proof of concept for it’s unnecessary. You’re project would execute much better in hard material.
Preliminary outsole concepts are commonly made out of hard non functioning materials before the real tooling.