please review the concepts manual: https://docs.oracle.com/en/database/other-databases/nosql-database/20.1/concepts/concepts-guide.pdf
Every application is different and needs to be tuned according to the needs of that individual application.
The concepts guide covers the general principals and the application developer needs to fine tune from there.
If you want specific assistance with your application, then Oracle support can assist but you will need to have purchased Oracle support for NoSQL. I can put you in contact with Oracle sales if this is something you are interested in.
Despite its name, the Storage Node Agent (SNA), which is what gets started with the "start" command you show above, is not responsible for actually managing data in the store. It is the Replication Nodes that do that. As a result, the SNA doesn't usually need a lot of heap space, and so the -Xmx64m and -Xms64m settings should be OK for real deployments. But we have seen cases, particularly where there are a large number of clients connecting to a secure store, where the SNA needs more memory. If you expect to have a large number of clients, then you may need to increase these sizes if you see OutOfMemoryErrors in the SNA.