The minimum cluster size is 3 worker nodes, 1 Master node, and 1 Cloudera Manager node, for a total of five nodes. The maximum cluster size varies based on cluster type and public cloud. Further information about this could be found in this Cloudera Altus Documentation section
NOTE: Each cluster spun up by Cloudera Altus requires 2 additional (master) nodes, one for CM and the other for Master services used for each cluster. These 2 nodes are a hard-requirement per cluster as they're required for a functional cluster and will need to be accounted for when calculating the public cloud instance limits.