Oracle server requirements calculation
You can roughly calculate current disk space requirements by using guidelines from the Oracle documentation, once you have defined your schema, including the necessary indexes and materialized views, if any. Do not forget to add space for backups and archived logs.

As for the CPU and memory requirements, they would mostly depend on the exact characteristics of your workload, given the schema defined earlier. In this day and age you should be able to spin up a virtual server with one of the cloud providers and run your load tests (you do have a load test suite, right?) against it much faster than trying to find some magical generic formula on the internets.