'I got 70 pieces of candy for Halloween!' - does this sentence look right? (I'm not sure about the word 'candy' and how to use it when I need to talk about separate pieces of candy)

US English?

"70 pieces of candy" makes sense and sounds natural. Sometimes it depends on the type of candy, and different countries or regions might have some differences, but this way sounds fine to me. Some people might say "a lot of candy" or "a lot of candies" but when mentioning a specific number, "pieces of candy" makes the most sense.

Yes, it sounds perfectly normal

It's fine (for American English).

This is natural sounding for my region. You could possibly also say "I got 70 candies" but this is slightly ambiguous as to whether you mean pieces of candy or types of candy and not as natural. Your version sounds better tbh