Re: Bulk loading
JanusGraph support for loading data does not go further than the Traversal API (used in https://tinkerpop.apache.org/docs/current/reference/#addvertex-step ) and the JanusGraphManagement API (used in https://docs.janusgraph.org/basics/schema/ ).
A better resource than the reference docs to get you started is:
The bulk loading tips will be useful for graphs with millions of vertices and edges.
Best wishes, Marc