Thanks for the detailed explanation of your use case. More interest in R is a great problem to have!
There are two strategies to consider for load balancing RSP users on specific nodes or groups of nodes.
1 - Custom Load Balancing in RSP:
There are different load balancing strategies that can be used with multiple nodes in RSP, and one of them is to use a custom balancing method that calls out to a script and passes details on the username and list of nodes. This could be used to balance users on specific nodes or a group of nodes but requires you to specify and maintain the logic for this to happen:
https://docs.rstudio.com/ide/server-pro/load-balancing.html#custom
2 - RSP Launcher:
Last week, we announced functionality in RStudio 1.2 that includes a Job Launcher that can start R sessions on external systems such as batch schedulers and container orchestration platforms. Launcher will initially ship with plugins for Kubernetes and SLURM, and additional plugins can be developed for other systems. In this case, you could handle the load balancing and access control by nodes in systems that handle this in a more scalable way:
https://docs.rstudio.com/ide/server-pro/1.2.1244-1/job-launcher.html
You might consider implementing approach #1 in the short term and planning to implement approach #2. Or, you could get started with approach #2 with the RSP 1.2 preview and see how it works for you:
https://www.rstudio.com/products/rstudio/download/preview/
Let us know how we can help along the way.