The biggest mistake I see founders make is planning infrastructure around user numbers instead of traffic patterns. A job board with 1M monthly users can be surprisingly lightweight if search is optimized and most traffic is read-heavy.

For me, I'd focus early on PostgreSQL indexing, query performance, connection pooling, backups, and basic monitoring before thinking about multiple servers. Most scaling pain arrives from inefficient queries and missing observability long before Hetzner becomes the bottleneck.

Also, if messaging becomes a core feature, that's the area I'd keep an eye on first rather than job listings themselves. That's usually where complexity starts creeping in.