Sorry, but I can't answer all your questions.
However, according to this article: http://nymag.com/health/features/46213/
, it says there's no need to get carried away trying to be barefoot all the time, but that it just helps the health of your feet and lower body to be barefoot sometimes.
I haven't gotten mine yet, but my plan is to transition to barefoot running before buying these. I'm hoping to start running on grassy football fields or tracks where I know the likelihood of stepping on a broken piece of glass or something is slim.
If you google plantar fasciitis, you should find some foot strengthening exercises, since PF is often caused by weak tissues in the foot.