in any means i ain't an expert, but by common sense and the medical/biological knowledge i have here are my answers (don't take them for granted):
1. in order to die from alcohol poisoning you'd have to get blood alcohol concentration over .5%. blackouts start at .2%, at .3% it gets difficult to stay awake, and onset of comas can start at .4%. also, there is a high probability you would simply throw up earlier and not be able to continue drinking (eg. bc of loss of coordination or blacking out)
2. mixing alcohol and SN will elevate the chance of throwing up - both of these substances make you already at risk of vomiting alone, let alone combined
3. opioids mixed with alcohol can increase the risk of lethal ODs. also, certain painkillers combined with alc can lead to respiratory depression, but i can't tell you which would guarantee certain death and what concentration should be used for that
4. in my opinion, this is a bad idea. the chance of dying from alcohol poisoning from drinking it in one sitting is low, additionally making the whole thing unpleasant. i would simply stick to SN - much more reliable and easier to CTB with