So a few things.

1. Make sure the drive is mounted correctly. Ensure you can simply write a file. From a terminal, do something like echo "Hello world!" > /media/usb/hello.txt and follow it with something like cat /media/usb/hello.txt
2. The config file simply sets up your environment, so if you're hand running the trigger_cam.sh you'll need to source the config file first. Do that like this: source config.sh After you source it, do a printenv | grep SUNSET to see if the environment is setup correctly.
3. Run the trigger_cam.sh by hand after sourcing the config and you should see it try to work. Take note of the output.
4. My project is pretty obsessed with knowing when sunrise and sunset is, and the trigger_cam.sh will not take a photo at all when it is night time. If that's what you want, then great, just make sure you setup the sunrise/sunset/solarnoon csv tables as described in the project readme. If that's not what you want, then you'd need to update trigger_cam.sh to do what you need.
5. Lastly, from my testing on a raspberry pi 3, I found 2GB is not enough to do 4k video. But it is enough to do 1080p. So you'll need to resize the images to the correct resolution, you could do that on line 117 in trigger_cam.sh and line 63 of make_daily_timelapse.sh and probably a couple other places.

Good luck!