Q1
For poller counts you would look at WorkerOptions->setMaxConcurrentWorkflowTaskPollers (default 5) and WorkerOptions->setMaxConcurrentActivityTaskPollers (default 5)
WorkerFactoryOptions->setMaxWorkflowThreadCount is setting for max number of actual threads available to be used for workflow executions across all workers created from a particular factory.
Q2
frontend.namespaceCount can be configured in dynamic config (default 1200). It can be filtered by ns and is typically looked at when you see resource exhausted issues for example:
RESOURCE_EXHAUSTED: namespace count limit exceeded
meaning there are too many concurrent polls for workflow/activity tasks to a single frontend host. So it has to do more with the number of workers, pollers and number of frontend hosts, rather than number of workflow executions (per namespace). No, dynamic config values cannot be updated from SDK.
Q3
Temporal server frontend service is for the large part responsible to route requests to history and matching service, and read the workflow event history for your sdk workers, so it is CPU heavy, yes.