Kvdb, system metadata and journal device

I am a devops engineer at Anaplan and have been recently working to get portworx on kubernetes running with pure storage in Datacenters with VMware hypervisors(I am not sure if mentioning VMware is relevant). I got an initial breakthrough were I was able to run all the portworx components successfully but I need clarification to effectively use it for our storage requirements and also in general about KVdb for better understading on how portworx utilizes them. For kvdb:

From the perspective of the storagecluster spec, I had a couple of questions:

  1. If I only define kvdbDeviceSpec and not others, does this take care of systemMetadata and JournalDevice as well?

  2. If I use these three specs separately:
    kvdbDeviceSpec, journalDeviceSpec, systemMetadataDeviceSpec, what should be the recommended allocation for each of them? I see that you have recommended metadata size needs to be about 64GB. Then what should be the recommended size for kvdbDeviceSpec with systemMetadataDeviceSpec set to 64GB?

  3. Considering I defined all three specs in the above question. If I have a cluster of 20 worker nodes, and I have only 3 kvdb instances. Does 3 kvdb instances mean 3 journal devices and 3 system metadata devices or they correspond to the number of storage nodes?