Thanks for this great write-up; I just put together a very similar setup. I used a StarTech 4-port serial “hub” I bought off Amazon (http://www.amazon.com/dp/B000YB0NQG/), since the one mentioned in this write-up I could not find in the U.S.; it appears to use the same FTDI chip-set.
One caveat I did run into is UDEV re-assigning what ports were mapped to /dev/ttyUSB*. I found this out the hard way trying to remotely configure a router and the port no longer worked. Turns out it moved. I found the article below to add UDEV rules to manually map a device symlink to the actual TTY based on the port 'serialID. This has worked well for me so far to keep device symlink the same while “following” what the kernel and UDEV decide to assign it.
http://hintshop.ludvig.co.nz/show/persistent-names-usb-serial-devices/