Well, Ted, I can't answer your real questions, but a bit ago, between the ages of 42 and 43 (I'm not 45 yet, fool!). acute posterior tibial tendonitis got me.
I could still get around, but I used (and still use) ibuprofen like crazy, and limping like a crazy fool. Not too much ibuprofren, but not too little: one of these days my gut's going to complain. Although I think the canonical medical advice is that the antinflammatory properties can take a few weeks of rigorous application/dosage to properly be effective. IOW, it's not an opioid where you take it and get instant relief. And the various devices to stabilize the foot. My favorite is just athletic tape.
There is, at least in the US, sold a product called KT-tape, i.e., "kinesio-tape," which comes pre-cut in large rolls, but I prefer the simpler rolls of generic athletic tape. It requires, as you know, a bit of knowledge and practice to apply correctly. The KT style of pre-cut strips is just for convenience, as far as I'm concerned, and being a bit stubborn, I just use regular athletic type that comes in a roll from you favorite pharmacy or drugstore or whatever. More fun to me, but YMMV.
Then again, what doesn't?
So, when I got that figured out, plantar fasciitis hit me hard. No amount of taping could help that, at all. except for taping to restore the arch of the foot, which for me relieved some of the presure. But, while they're not official orthotics, I found supporting the arch with over-the-counter sole inserts help.
That, rest, and lots of ibuprofen. And for the plantar fasciitis, doing the recommended stretches at home.
That last bit was really the key: once the pretty severe pain subsided a few hours after waking up and sitting at my desk drinking coffee, just a gentle elongation of the fascii alongside another desk in my my office.
What bothered me, aside from the nearly-delibitating pain and the finicky regimen of NSAIDs, was that it was difficult for me to do pushups, which I like to do.
No, I don't have any advice for you, but just a reminder that you should have courage, mon vieux.
I really do think if you catch PFasciitis early enough you can work through it, mostly by careful elongation of the fascii, plus rest. but I don't believe there are any special home remedies I know of: just rest, elevation.
And, yes, this sounds crazy, but I like the epsom salts soaking of the feet.
Now I'm officially old. Thank you very little!
About the spasms in muscles, the ony thing is a cramp in either of the hands, that, while not painful, makes it impossible to use either hand for about a half an hour so.
I suspect it's neurological in basis, in my case, ad the latter, but I really wouldn't know.
I do think over-the-counter insoles can lessen the need to use athletic tape, about which latter, as you know, there are specific techniques for applying the tape.
I don't know anything about flat-feet, though.
But the acute, sometimes crippling, pain of plantar fasciitis has far exceeded anything, even beyond an ankle I either broke or sprained or strained recently.
No, for that, I found the only remedy was careful stretching/elongating the fascii. Not even prescription-strength ibuprofen helped. Absolutely debilitating, and it last about eight months.
The worst, though, was just like postTib tendonitis, not being able to put my foot on the floor to do pushups.
And that is my greatest shame, never have been able to circumvent the problem by doing one-handed push-ups: not that those are all that difficult, but that' a variant one of of my favorite exercise just to do whenever a free moment finds itself open to me.
Drunk, sober, bored: I love doing pushups, and these ailments really made it extremely difficult.