...except in a sentence like 'How much hot milk do you want?'
Indeed!
It doesn't work before an adjective on its own, when the adjective does not precede a noun.
True.
Even in cases where 'much' can, if formally, be used as an intensifier (e.g. I was much surprised to learn...) we still wouldn't ask *how much surprised?.
You don't hear "much surprised" very often in BrE these days.