As with any other server software, the requirements for a Pimcore installation depend on the expected load and the amount of data to be processed.
Especially the generation of image variants and regular data imports need sufficient capacities. For starters, we recommend at least 2 CPU cores and 4 GB RAM in combination with Redis as cache. Without Redis, 2 GB RAM is also sufficient. As an operating system, Ubuntu v14.04 or higher has proven itself to us, 16/Xenial is optimal. The general software requirements of Pimcore can be found at https://pimcore.com/docs/pimcore/current/Development_Documentation/Installation_and_Upgrade/System_Requirements.html, further information on hosting and installation is here: https://pimcore.com/docs/pimcore/current/Development_Documentation/Installation_and_Upgrade/System_Setup_and_Hosting/index.html