I would use Reticulum instead of Meshtastic. https://reticulum.network
Pros: - it can actually scale past 20 devices - Forward secrecy encryption - Is designed to support multiple underlying transport systems such as TCP or LoRa - Announce based routing rather than flooding the entire network which is order of magnitudes faster Cons: - Not as many nodes as Meshtastic has - Python implementation with no C implementation (can be speed up with cython however)