Integrations on remote Raspberry Pis

I have HA running on a server in my server room. I would like to connect some devices (solar inverter, alarm, etc.) that have HA integration, but require physical connection to HA host - they are connected via RS485/RS232 serial ports or some have USB port only. However they are scattered around my property and there is no way I can connect them all to a single host. I have ethernet at all locations, but the distances don’t allow for direct copper connection (I have direct fiber optics though).

I found some posts about using MQTT to communicate between HA host and the remote RPi, but that was always for zigbee and I don’t see a way to run HA integration that way.

I know about converters that can turn serial ports into IP traffic and another one that makes it serial again, so I could buy a pair of these to get all the serial lines to the server room.
The devices with USB ports will be a bit tricky, but so far they are all just serial ports over USB, so I believe it should be possible to connect them to RPi running regular Linux and then tunnel the serial port over SSH to virtual serial port created on the HA host.

Is this the correct approach to this problem? Are there better ways I couldn’t find? Or are there ways to run HA integrations remotely?
Thank you.