Yes, with it you won't be needing an extra sedative like benzos because it works as an antipsychotic.
As for the dosage, studies have been made proving that 5mg works as an antiemetic to resolve nausea caused by chemotherapy but since this is SN that you're probably planning on using considering the question you asked, I think the most reasonable dosage would be about 10-20mg, depending on your tolerance to the medication and how it interacts with your body.
EDIT: Here is a thread made by someone who succeeded with SN using Olanzapine as an antiemetic. You can use this as some reference, if you want.
Started my fast 6 hours ago I will be updating I hope it will be helpful for those who need it. Method is SN I will be taking paracetamol and olanzapine
sanctioned-suicide.net