More resources are always better, from the configuration of a single Crate node as well as the number of nodes in a cluster. For a useful production environment you should have several GB of RAM, 4 cores, and a decent SSD drive per node. We recommend at least a five node cluster if resilience and performance are important.
The absolute minimum requirements are a single core, 40 MB of RAM for the application and a disk. Several independent host nodes are recommended, but a small Crate cluster runs on a single developer machine for testing purposes.