There are no limits on the type of hardware used to host an eFront installation. However, as your needs grow, so will the need for additional resources.
A bare-bone eFront installation requires about 50M of free disk space and 64M of free system memory. However, a minimum of 128M free memory available to PHP is recommended. Disk space should be allocated according to usage.
For small installations (up to 100 users/20 simultaneous), a simple server with 1GB RAM should be sufficient. Doubling the RAM is recommended for double the usage (200 users/40 simultaneous).
This rule of thumb is convenient for up to 1000 users/200 simultaneous. For usages higher than this, it is recommended to physically separate the database server from the web server.
Using SSD disks, especially for the database server, will considerably boost the overall performance.