Welcome to the MySensors forum. MySensors is a library you can use to create a wireless mesh network of sensors which communicate with a central point, such as your Raspberry Pi. You could attach an Arduino Nano to USB and talk to it via Serial. You could create a MySensors network, which you could also communicate to via an arduino+radio on your USB port. Then you could attach countless sensors. There is a ready-to-go sketch for the MH-Z19B.