Istio Service Mesh rollout into Prod (Design / Architectural decisions)

This is more of a design architectural decision to rollout Istio Service Mesh solution into Production. What are the key design decisions to make in this regard. What were the learnings/outcomes after rolling out into Prod. We are considering using Istio Operator as the way to go which would reconcile the state of the service mesh and possibly it would be a service mesh on boarding different k8s(v1.13.12) clusters gradually.