[mitchellh]

We recommend three or five because that will get you a high level of fault tolerance. Consul runs just fine with one server, but you'll have no fault tolerance: if that one server becomes unavailable for any reason, then reads/writes for your cluster will not be served.

The leader is elected using Raft as the consensus algorithm (it is linked in the internals section of the docs).

You are correct though that if you run multiple servers, the leader election will happen automatically. There is no way to manually override it.