Minimum system requirements are 2 vCPUs, 8GB of memory, and 100GB of disk space (as of version 184.108.40.206). However, these are just minimum requirements.
It is recommended to scale up for higher workloads and add additional disk space if you are going to receive and send higher volumes of mail.
Monitoring of your eFa is important to ensure that adequate resources are available.
There are currently 3 options to deploy eFa, deploying on of the VM image is the most common way to start with eFa.
If you don't have the option to deploy an Virtual Image (on some VPS hosters for example) you can build eFa using the build scripts.