Assuming you can afford enough hosts, is the best setup for an index a single shard with a complete replica on each node?
Best for what use case?
Setting up a cluster for internal use to monitor log events (2-3million documents a day). Making data available to users via Kibana to do aggregations, user counts, click counts, etc.
Unless you need super fast performance then no, it's probably not ideal and is just a waste of resources.