Confirmed, for the exact use case described (internal, self-hosted, no sharing with third parties), there are no costs. The n8n Sustainable Use License explicitly permits this.
One thing to keep in mind for the future, in case your use case changes: As soon as you host n8n for external customers (i.e., let other companies use your n8n instance) or embed it in a product you sell, the license no longer applies. The exact wording can be found here: n8n/LICENSE.md at master · n8n-io/n8n · GitHub , it’s worth bookmarking before your use case grows.