All of the above will not only maintain strength, but cardio-vascular fitness while the patient heals. Not infrequently, the original problem of plantar fasciitis will respond to new shoes because of the added cushioning in the heel. It is essential that the heel portion of the running shoes fit the individual exactly. Too wide a heel will cause excessive motion of the fat pad that cushions the heel bone, and will allow the fat pad to spread out, causing it to be shallower than if a narrow heel counter supported it. It's ice, rest, cushioning and stretching.
Many people have a heel spur on x-ray.
Most of us do not feel it has anything to do with heel pain. It's the inflammation of the plantar fascia that is the culprit. No, there's no formula as to number of hours of sleep as relates to the amount of mileage a person is running. However, rest is essential in training for any long distance running event. There is no good evidence to suggest that more moderate physical pursuits are any less suitable in promoting cardio-vascular health, and there is an abundance of research suggesting that the human body is incapable of surviving the repeated stressors placed upon it by running marathons.