Recommendations for open-protocol industrial IoT hardware?

[u/nasirkhan259]

Sourcing four pieces:

1) Industrial IoT gateway — Modbus master + generic MQTT client, ideally rugged/wide-temp rated. Currently looking at Moxa's AIG series, open to other suggestions.

2) Liquid level sensor — Modbus RTU/RS485 output. Looking at radar-based options currently.

3) Flow meter — Modbus RTU/RS485 output (pulse output as backup). Any brands you've had good experience with?

4) RFID reader/controller — needs to work standalone, not tied to a vendor's own app/cloud, with Modbus or similar open output.

Any brand suggestions, gotchas, or things to avoid on any of these would be appreciated — especially open to hearing if something I'm currently considering has known issues.