Overall it makes sense. Not sure if you've seen it already, but this reference architecture is similar to what you're building: https://learn.microsoft.com/en-us/azure/architecture/example-scenario/integration/app-gateway-internal-api-management-function

Some comments:

SPOF concerns can be mitigated by onboarding availability zones to be protected from compute failure. Configuration deployment failures can be prevented by controlling your dev process.

Look at v2 tiers to have lower provisioning and scaling time: https://learn.microsoft.com/en-us/azure/api-management/v2-service-tiers-overview#key-capabilities