I am pretty sure that the word candy can be both countable and uncountable. (How many candies did you eat last night vs How much candy did you eat last night?) My feeling is that it is more commonly used as an uncountable noun. Am I right?
uncountable...How much candy did you eat last night?)
Lots. Some. None. When I count zeros I end up with none.
The only way I would consider candy to be countable is if referring to types of candy, not pieces of candy.
How many candies did you eat last night? I ate three kinds: caramels, chocolates, and taffy.
Generally, I think of candy as uncountable and would have to say "pieces of candy" to answer how much candy I ate.
OP and #1 are correct in my opinion, at least for the US and the UK. #3 "candies" can be used in the sense you indicate also, but need not be restricted to that sense.
CK

What chriskean said, with the addendum that I don't think anyone would understand "How many candies did you eat last night?" to mean "How many types of candy?" "How many candies does Necco produce, besides Necco Wafers?" would be so understood.
I wouldn't actually ask, "How many candies did you eat last night?" or immediately understand that it means types of candy if asked in real life. However, since my experience is that candy is not used as a countable noun for pieces of candy, that is the only meaning I could attribute to it in this discussion. I would understand "How many candies does (name of candy store) sell?" to mean types of candy, though.
Other people may use candy as a a countable noun referring to individual pieces of candy, and I see that that definition is included in dictionaries, but that has not been my experience.