FileMaker Server 19 specifications can be found at https://community.claris.com/en/s/article/FileMaker-Server-19-System-Requirements
FileMaker Server 18 specifications can be found at https://www.filemaker.com/products/filemaker-server/18-technical-specifications.html
Please observe that a SSL certificate is mandatory.
Contact us to hear if it can be provided by us or if you need (or want) to provide it yourself.
FileMaker Server 17 specifications can be found at https://www.filemaker.com/products/filemaker-server/17-technical-specifications.html
For hardware requirements, we strongly recommend those listed under "Recommended requirements". Furthermore we recommend a disk setup with three disks. For more information go to System architecture