32 bytes (256 bits) is used internally IIRC. More provides no additional security. Only use more if you have a need for more key output for reasons specific to your application.
crypto_scrypt() allows me to specify how much data I want back from it.
This is what the last parameter, buflen, is for.
So the question is, how many bytes should I request to make it good for
hashing, just as good as SHA-256 say? Purpose being to make collisions
virtually impossible.
For example, are 200 bytes enough?