Use the latest release of PostgreSQL. Replication features are changing fast, with each new release improving on the previous in major ways based on our real-world experience. The idea that earlier releases are somehow more stable, and thus more easily usable, is definitely not the case for replication.

Use similar hardware and OS on all systems. Replication allows nodes to switch roles. If we switchover or failover to different hardware, we may get performance issues and it will be hard to maintain a smoothly running application.

Configure all systems identically as far as possible. Use the same mount points, directory names, and users; keep everything possible the same. Don't be tempted to make one system more important than others in some way. It's just a single point of failure and gets confusing.

Give systems/servers good names to reduce confusion. Never, ever...