Hi. I've never tried Five Fingers, but I have had problems with plantar fasciitis, in both feet at different times.
During my most recent bout with PF, I found that wearing MBT (Masai Barefoot Technology) (aka "rocker bottom") shoes allowed me to walk WITHOUT PAIN! And helped my PF to clear up, finally. The MBT's don't really give arch support, but they make your foot deal with random orientations that promote strengthening of the foot muscles.
Good luck with your PF. I did get one cortisone shot into my foot that did help.