What determines the result is how fast the onset symptoms are and how soon they get to ER and receive medical treatment. You don't have to take 100g when the regimen is there to be followed for a reason, you don't have to exceed the amount of 20-25g, it'll be just as lethal plus taking a higher amount doesn't guarantee you will ctb, you may end up vomiting all of it out. Your last question makes no sense about what could induce Methomoglobinemia before taking sn, there's SN to take for a reason to induce that, you don't need to worry about anything else, it'll be deadly enough by itsel. Also, what do you mean you'll be taking SN without a regimen when it's required to follow a basic fasting protocol even if you don't have the required meds.
I'm going to stress to just keep things simple, do not think of deviating a method that has worked as it is by itself without any unnecessary changes. Do not drink alcohol either, it won't help at all with the process in its entirety. If you deviate from the method then you are only going to increase the chances of failure being the end result. Keep it simple, make sure your sn is pure enough, fast for 8-15 hrs or however you feel is long enough to maximize absorption and if you are worried about the taste, get something such as mint to deal with that. That breakdown I just gave is about as simple as it gets.
Again, SN by itself will be just enough to rapidly cause Methomoglobinemia, you do not need to do anything outside of this. To Maximize success is to look at what is the most common cause of failure with this method and mitigate that especially when you apply it to your own circumstances.