I am an experienced Java developer and architect, and I've worked previously on Cassandra 1.x and 2.x. I also know JPA, which is used here.
In principle, this project is well defined. The only complexity is that the current schema requires joins, which are not supported in Cassandra. I am confident I can define a compatible alternative.
I would be happy to discuss details with you, which may result in adjusting my bid.