I'm a big fan of the Home Assistant Project, which has a framework for ESP-based devices called ESPHome. The framework allows the devices to be easily integrated into Home Assistant, with data collected and written into its SQLite database. Home Assistant allows the use of other DBs, such as MariaDB, where a JDBC connection can be set up. A scripted REST API could be made in SN, and Home Assistant could push the data using Node-RED, which has similarities to Flow Designer. This is, of course, an alternate solution to what you have implemented.