Sorry, I am not clear about what you are trying to solve.
Warm needs to have space for primary and replicas...
Not sure what you mean by other sites etc...
You DO need to use routing if you have multiple warm nodes in each zone to ensure the primary and replica are in different zones... I *think this happens automatically if you have set up ECE properly across AZs
BTW you have ECE so by definition, you have Support so you can ask that.