typedef all structs - yes, helps with conciseness. Use typedefs liberally, I say. But only typedef the things themselves, not pointers to the things. You can always use (type *) when you need a pointer. In particular, for function pointers, typedef the function, not the function pointer. Then you can use the function typedef for function declarations too, which gives you parameter type checking without needing to fix declarations everywhere if you change a function signature. I see most C codebases get this one wrong, typedef'ing the function pointer and still needing to manually write out all function declarations for that pointer definition.

I'm not sold on the structs as return types thing. I prefer just a numeric error code as a return value, and out parameters for any other returns.