@Rustictomato, you should create a test business with just a few inventory items and conduct experiments so you can understand what happens with every type of transaction without jeopardizing your real accounting records. You have so many questions, those trying to help you will get lost in the details. And the potential for misunderstanding is high due to the different ways people use terms. See the Guide:
https://forum.manager.io/t/experiment-with-a-test-business/7067