From this link:
Minimum Hardware Recommendations
For production use, the computer on which you install or upgrade Tableau Server should meet or exceed the minimum hardware recommendations. These recommendations are general. Actual system needs for Tableau Server installations can vary based on many factors including number of users, and number and size of extracts.
Free Disk Space
8-core, 2.0 GHz or higher
Multi-node and Enterprise deployments
Contact Tableau for technical guidance.
Nodes must meet or exceed the minimum hardware recommendations, except nodes running backgrounder, where 4 cores may be acceptable.
I believe 8 CPU core should be sufficient but I'd double the RAM and Disk Space in the table above (minimum hardware = minimum performance).