Temporal multi-tenancy

I’m currently investigating the implementation of multi-tenancy on the Temporal cluster, considering the choice between having one tenant per namespace or allowing multiple tenants per namespace.
I currently have a preference for multiple tenants per namespace, because some of workflows are shared. I am expecting <= 50 tenants

As I make this decision, I have a few questions:

Q: In the one tenant per namespace model, how do client create a workflow that can be shared?

Q: Could a heavily loaded namespace negatively impact the performance of another namespace?

Q: In the multiple tenant per namespace model, can workflows running for tenant A affect the performance or resource availability for tenant B within the same namespace?"