Interesting project, thanks.
I was considering something similar myself, but at the moment am working with an off the shelf remote serial solution. A benefit of this approach is that you get the full functionality of the current integration, e.g. sensors support.
I’ve used a couple of devices from https://www.pusr.com/ . They do a range of Ethernet and Wifi devices that can support TTL, RS232 and RS485.
For this project I selected Serial to Ethernet Converter Modules | Ethernet UART Modules and paired it with a MAX3485 3.3V Powered, 10Mbps and Slew-Rate Limited, True RS-485/RS-422 Transceivers | Maxim Integrated. I chose these so I could get them inside the JA-8x control panel (I have a JA-82K). You will also need a 5v or 3.3v power supply, I used a step down transformer such as https://www.amazon.co.uk/Converter-Reduced-Voltage-Regulator-Interface/dp/B08VHZJ3C8/ . The cost of these is around £20 and no other components are required (though some may recommend some capacitors, I’m no expert here)
An easier method if you don’t care about fitting it in the case is Ethernet to Serial Converters | Converter Serial to Ethernet, which costs around £30. This can run off the JA-8x power too, so no additional plugs needed.
Lastly, the very simplest is to use a 1-port RS485 to Ethernet Converters | Ethernet to RS485 Converters | RS485 to TCP IP Converters this needs an external power supply/plug and only requires 2 wires (for the RS232 connection) to go inside inside the control panel onto the A and B terminals.
All of the above are workable for a novice IMO, well, anyone happy to play around inside the control panel as I imagine most of us on this thread are.
This can be used with the JA-8x integration here GitHub - tahvane1/jablotron80: Jablotron 80 integration for Home assistant