Good morning, and welcome to 3D Printing SE.
You said: "I can see information from the printer via USB in RepG and through OctoPrint, but can't send any prints, commands or upgrade firmware (I wanted to flash Sailfish 7.7 eventually)." This means that the USB communication is working fine. It isn't a question of drivers or the FTDI interface chip. That ...
You can find gcode information at the RepRap wiki. The obvious other thing to try is G1 X10 for a move.
Octoprint prints by sending the individual file's gcode one line at a time over USB. It appears that the firmware on your printer might not respond to any 'action' commands over gcode, rather than any fault as such with your hardware/software setup.
It is possible that your board has a cloned FT232R USB-to-serial bridge chip, and FTDI drivers supplied via the Windows update channel will not work with cloned chips. Try using the Windows setup executable from the following page:
FTDI Chip: Virtual COM Port Drivers
Note that there are no known problems with MacOS and Linux drivers.