Heel pain/plantar fasciitis/collapsed arch, what to do?

Orthotic. I would advise a good custom molded functional foot orthotic. We have them made all the time and patient's with your symptoms do very well. .
See a podiatrist. You present a difficult problem that needs an exam. It is most likely that you will need orthotics to control the motion of your foot and support the arch but you may need more extensive treatment to get rid of the plantar fasciitis.