Sort:  

great! I assume libsecp256k1 will be used for the actual signing?
Do you know the network wire protocol? iguana likes to be at least a passive peer so it can submit the signed transaction directly

Please see my other comment for the network "code".
Afaik @void is usint libsecp256k1 .. if not you can see how the python code is doing it since it calls the native libspec256k1 methods as well (assuming the req. libraries are installed)