I don't know the specifics, but I have read somewhere here that ingesting heroin and opiates through snorting/orally has lower bioavailability compared to IV, plus there's the risk of vomiting the stuff back up (at least when taken orally, dunno if it can also happen with snorting) that you need to take into account with something like an antiemetic.
I've heard of plenty of cases of accidental deaths through Heroin OD, but not only am I pretty sure most of it was done through IV, it wouldn't surprise me if some of it was also cut with fentanyl, which is far more deadlier than heroin if you have little to no tolerance to opiates/opioids. If you plan on getting your heroin through the dark net, I wouldn't count on it being cut with fentanyl. Loads of places on the dark net are trying to crack down on fentanyl, including stuff cut with it, so I wouldn't bet your hopes on getting some heroin cut with fentanyl. But if you do want to take a gamble, I've read china white heroin is the most likely to be cut with fentanyl.