There's no way to tell for sure what will happen. You may vomit, you may not. I think the important thing is if you do vomit then immediately take the second glass or abort and call for help.
If you vomit whilst unconscious then it's entirely down to luck. You may have ingested enough SN to kill you, you may choke to death on your own vomit or you may wake up very much not dead.
The benzo dose is complicated, I also struggle with it. Like you I have a low tolerance to them so doesn't take a lot to really affect me. I'm just wary of a failed attempt because the benzos took me out too soon and I vomited the SN out.
I agree with this completely. If you take enough benzodiazepines to pass out, if you do vomit, you'll not have a chance to drink a second glass or abort.
If you are benzo naive, you might want to experiment first to see how many you can take before you fall asleep.
I have Xanax. I'm struggling with how many to take as well. I think I'm just going to take 1 or 2 mg an hour before for the calm and to help fight SI. I don't want to fall asleep.
While it would be great to be knocked out within minutes due to a benzo OD, I don't think the risk to overall success is worth it, personally. Let's be real: SN seems like a good method overall, but it's not N.
As a note, benzodiazepines have some antiemetic effects.