You do not need Consul Enterprise in order to deploy your proposed 3 node cluster.
When Consul is deployed across multiple AZs, Redundancy Zones help Consul maintain quorum in the event of server failure in an AZ by automatically promoting a non-voting server to a voting server. The Consul Enterprise Redundancy Zones page on Consul.io provides a better description of this feature.
Consul Enterprise redundancy zones make it possible to have more servers than availability zones. For example, in an environment with three availability zones it’s now possible to run one voter and one non-voter in each availability zone, for a total of six servers. If an availability zone is completely lost, only one voter will be lost, so the cluster remains available. If a voter is lost in an availability zone, Autopilot will promote the non-voter to voter automatically, putting the hot standby server into service quickly.
Redundancy Zones are not required to deploy Consul across multiple AZs, but the auto-promotion provided in Consul Enterprise can be of value to organizations who are looking to reduce operational overhead & downtime incurred during outage scenarios.