Bear in mind that you won't be able to merely "tune" your schema - you will need to completely redesign your data model. Step one is to look at all of the queries you need to perform and get a handle on what flat, denormalized data model they will need to execute performantly in a NoSQL database. No JOINs. No ad hoc queries. Secondary indexes are supported, but not advised. The general model is that you have a "query table" for each form of query, with the primary key adapted to the needs of the query. That means a lot of denormalization and repetition of data. The new, automated Materialized View feature of Cassandra 3.0 can help with that a lot, but is a new feature and not quite stable enough for production (no DataStax Enterprise (DSE) release with 3.0 yet.) Triggers are supported, but not advised - better to do that processing at the application level. DSE also supports Hadoop and Spark for batch/analytics and Solr for search and ad hoc queries (or use Stratio or Stargate for Lucene queries.)
Best to start with a basic proof of concept implementation to get your feet wet and learn the ins and outs before making a full commitment.
Is this a Java app? The Java Driver is where you need to get started in terms of ingesting and querying data. It's a bit more sophisticated than just a simple JDBC interface. Most of your queries will need to be rewritten anyway even though the CQL syntax does indeed look a lot like SQL, but much of that will be because your data model will need to be made NoSQL-compatible.
That should get you started.