I’ve noticed its possible to install USB devices with drivers and packages, but AR300M only has one and I wanted to use it for USB tethering plus more devices, is it possible to use a USB hub to use multiple devices for them one USB port? I noticed modules like 5G are add ones is a Bluetooth module add-on possible?
Yes, you can connect a USB hub and connect more USB devices without problem.
But you need to configure them by yourself. For example, if you have two modems, you need to config which modem to use or use load balancing. If you use different devices, e.g. one modem, one usb drive, one bluetooth module, they should just works fine.
Be sure to check the power consumption. If these consumes a lot of power, please use a hub with power supply.