Hey @fast-vr-6049. I am not any kind of expert at all. But I'll give you an educated guess. ;)
What I've found using the azure-native package is that if the ARM template for a resource accepts a certain value, and the corresponding Pulumi property isn't something like an enumeration (i.e. it's a string), then you can set that Pulumi property to the value that the ARM template accepts.
If I'm working on a new type of resource for the first time and am not sure about anything, I'll create the resource exactly as I want it using the Azure portal (in something like a "research" resource group so it's easy to discard and won't conflict with the Pulumi program). Then in the portal I'll look at the ARM template for the resource. From there I can usually reason to what I should set the Pulumi property to.
None of that is specific to an Event Hubs Namespace. Sorry.