The foot/toe pain sounds similar to mine. I take calcium and occasional potassium, but prefer to get the potassium from foods like bananas. I also stretch my feet when I can, but they are still quite touchy. A few mornings ago, I got out of bed and went to feed my cats. Just from the simple stretch to put the cat food down on the deck, my foot suddenly lost sensation and I knew the next thing would be cramping, so I quickly began to gently walk on it until it was normal again.
I also have a very high foot arch, and absolutely have to have soft arch insoles, or I'm 'doomed.' It helps me to wear very supportive shoes with lightweight but thick soles (not always easy to find!). I have a pair of gel-soled tennis shoes which are the best (ASICS, I think?). I need another pair! I can only wear sandals or go barefoot for a short time or my toes tend to cramp, or else my arches do. Even in the bathtub or shower, I have to wear lightweight socks going in and out (careful of the soles if you try this so you don't slip!)
Drinking lots of water throughout the day also seems to help.
I wish I could wear the Birkenstocks like Sherrine has, but whenever I wear a hard sole, my feet get stubborn and go into a cramp.
Best guess is that this is more about my undiagnosed-as-yet neuro condition, rather than the fibro.
Hope you find relief soon! Oh--and I also try to alternate sitting and standing when/if possible.