I managed to fix a similar "cannot find module" problem by running the module NPM command (e.g. for MQTT it was "npm install mqtt --save") in the directory where my Script resides ( e.g C:\Users\MYUSERDIRECTORY\tessel-code.)
After running the NPM command, another directory called "node_modules" was created which contained the bits needed (e.g. for me it was the MQTT library). Thereafter, running the "T2 run xxx" worked fine to completion
As for using the power USB connection for serial communicatino like as with an arduino, I'm not sure it can be done, because the USB connection doesn't seem to be recognised by any terminal program.
These links have more info about using other pins for UART comms
For that, you could use something like a "USB2.0 To TTL 6Pin CH340G" (use this phrase to google it)