that's a good question, i know that there are many characters that share one pronunciation, but i have not come across the reverse. there are different pronunciations in different dialects/languages of course, and maybe some of those get adopted by other dialects (that would make sense for food names for example) but i didn't study chinese, so i really don't know.

Mostly yes. In Mandarin, tone can be a bit different depending on context but overall pronunciation doesn't differ that much.

But a major caveat is that pronunciation can be wildly different when spoken with other dialects. Mandarin and Cantonese reading of the same text, even with same meaning, sound entirely different.