Dear Sir,
I would like to contribute in your PLC project. My recommendatipon is to use Siemens S7-1200 PLCs or automation Direct ClickPLC for this work. All the listed monitoring and control functions can be readily implemented in these PLCs, including Ethernet link (which the Omron CJ1M lacks). Your field sensors should have appropritate transmitters (4-20 mA, or 0-10V). The Supervisory BMS needs to fetch data from this PLC through Modbus.
I can provide you electrical schematics for the system, and also program the PLC. I assure you that it will be cost-effective and will require much less time to develop (compared to custom made embedded systems).
Looking forward to an exciting project. Best regards.
Yeasir Rahul